Since this bug exists for a very long time now, here is an easy way to patch it up without much of a hassle:

1) Right click on the game and select 'Manage' then 'Browse local files' and go to 'hl2mp\cfg'.

2) Create a file named 'autoexec.cfg' (if this file exists then you can skip this step).

Open your favourite text editor (e.g. Notepad).

Go to 'File' then select 'Save as...'.

In the 'Save as...' dialog in the 'File name' input 'autoexec.cfg' and in the 'Save as type:' select 'All Files' then click 'Save'.

Close the text editor.

If everything went well then you should have a file named 'autoexec.cfg'.

Place it in the 'hl2mp\cfg' folder we opened in step 1 (if you are a more advanced user you can also create the 'autoxec.cfg' file directly in '..\hl2mp\cfg').

3) Open the 'autoexec.cfg' with a text editor (the file should already be opened if you created it directly in '..\hl2mp\cfg').

4) Add the following lines to the file:

cl_playermodel "models/humans/group03/male_01.mdl"
cl_logofile "materials/vgui/logos/spray_lambda.vtf"

alias "rebels" "cl_playermodel models/humans/group03/male_01.mdl;jointeam 3"
alias "combine" "cl_playermodel models/combine_soldier.mdl;jointeam 2"

bind "F9" "rebels"
bind "F10" "combine"
bind "F11" "spectate"

5) Save the changes.

6) (optional) Make 'autoexec.cfg' read only.

7) Start the game.

Now, you can use the F9 button to join the Rebel forces, the F10 to join the Combine forces or F11 to simply Spectate any match.

Let's see now, line by line, how the 'autoexec.cfg' code works.

In the first 2 lines, we set the default player model and spray.

cl_playermodel "models/humans/group03/male_01.mdl"
cl_logofile "materials/vgui/logos/spray_lambda.vtf"

In the next 2, we set the model we want to use when we join the corresponding team. We also give, at the same time, the long commands like 'cl_playermodel models/humans/group03/male_01.mdl;jointeam 3' a shorter command name (alias) to use later in the code.

alias "rebels" "cl_playermodel models/humans/group03/male_01.mdl;jointeam 3"
alias "combine" "cl_playermodel models/combine_soldier.mdl;jointeam 2"

Finally, in the last 3 lines, we bind the short command names (aliases) of the previous 2 lines to the corresponding buttons.

bind "F9" "rebels"
bind "F10" "combine"
bind "F11" "spectate"

Note that the 'spectate' command name is game built in and we don't need to write code for this one.

You can always set your preferred default model, spray or your preferred model when joining a team by editing the model name in the code above. Bear in mind though that the preferred model when joining a team MUST correspond to the respective team (for example, don't use the 'police' model with the Rebel team).

For easy reference, here is a list with the player models and sprays that can be used as the preferred ones in the code above. An example on how to use these lines in our code will follow in the next chapter.

Rebels

models/humans/group03/male_01.mdl - Male rebel Van.
models/humans/group03/male_02.mdl - Male rebel Ted.
models/humans/group03/male_03.mdl - Male rebel Joe.
models/humans/group03/male_04.mdl - Male rebel Eric.
models/humans/group03/male_05.mdl - Male rebel Art.
models/humans/group03/male_06.mdl - Male rebel Sandro.
models/humans/group03/male_07.mdl - Male rebel Mike.
models/humans/group03/male_08.mdl - Male rebel Vance.
models/humans/group03/male_09.mdl - Male rebel Erdin.

models/humans/group03/female_01.mdl - Female rebel Joey.
models/humans/group03/female_02.mdl - Female rebel Kanisha.
models/humans/group03/female_03.mdl - Female rebel Kim.
models/humans/group03/female_04.mdl - Female rebel Chau.
models/humans/group03/female_06.mdl - Female rebel Naomi.
models/humans/group03/female_07.mdl - Female rebel Lakeetra.

Combine

models/police.mdl - Civil Protection (Metro Cop).
models/combine_soldier.mdl - Combine Soldier.
models/combine_soldier_prisonguard.mdl - Nova Prospekt Prison Guard.
models/combine_super_soldier.mdl - Combine Elite.

Sprays

materials/vgui/logos/spray_canned.vtf - Can in the trash.
materials/vgui/logos/spray_combine.vtf - Combine logo.
materials/vgui/logos/spray_cop.vtf - Metro Cop.
materials/vgui/logos/spray_dog.vtf - Dog.
materials/vgui/logos/spray_freeman.vtf - Freeman face.
materials/vgui/logos/spray_head.vtf - Headcrab.
materials/vgui/logos/spray_lambda.vtf - Lambda logo.
materials/vgui/logos/spray_plumbed.vtf - Toilet hitting player.
materials/vgui/logos/spray_soldier.vtf - Combine soldier head.

Let's see now an example on how to use the models above.

Let's say we want to use 'Female rebel Chau' as our preferred default model, 'Dog' as our default spray and also use 'Female rebel Chau' again as our preferred model when joining the Rebels team. Our code will become like this:

cl_playermodel "models/humans/group03/female_04.mdl"
cl_logofile "materials/vgui/logos/spray_dog.vtf"

alias "rebels" "cl_playermodel models/humans/group03/female_04.mdl;jointeam 3"
alias "combine" "cl_playermodel models/combine_soldier.mdl;jointeam 2"

bind "F9" "rebels"
bind "F10" "combine"
bind "F11" "spectate"

Let's take a closer look at the changes we made to our code.

We replaced the line

cl_playermodel "models/humans/group03/male_01.mdl"

in our original code with the line

cl_playermodel "models/humans/group03/female_04.mdl"

to use 'Female rebel Chau' as our preferred default model,

the line

cl_logofile "materials/vgui/logos/spray_lambda.vtf"

with the line

cl_logofile "materials/vgui/logos/spray_dog.vtf"

to use 'Dog' as our default spray

and the line

alias "rebels" "cl_playermodel models/humans/group03/male_01.mdl;jointeam 3"

with the line

alias "rebels" "cl_playermodel models/humans/group03/female_04.mdl;jointeam 3"

so that 'Female rebel Chau' will be used as our preferred model when joining the Rebels team.

The same applies for the other models as well.

Well, hope I helped things a little bit...

Have fun!

P.S. Don't forget to give this guide a thumbs up, if you found it useful. :)