Hm, apparently there's an error when you simply enable a third button.. yes - it was in NAbomination but I think it's worth mentioning here for future reference - it's most likely game's logic and NAbomination only allowed to notice this.
It appears that while it had third button enabled, there was a problem with mission progression for Yuri's campaign. After every completed mission the game wanted to execute Tiberian Sun's leftover mission selection screen which lead to an internal error.
I managed to get progression working just fine. I suspect this issue affects all sides, but ThirdSide doesn't normally have sidenc03.mix (or whatever the map progression mix files are called) present while GDI and Nod do have the relevant file. IIRC I copied sidenc02.mix to sidenc03.mix and that solved the problem (along with relevant entries in mapselmd.ini).
Code related to this issue has just been checked in!
Author: AlexB
Location: issue-202-third-button, r682
Revision comment:
Fixed issue #202: Enable "Third Button" on campaign selection menu.
Refer to the documentation to see how to enable it.
Code related to this issue has just been checked in!
Author: AlexB
Location: issue-202-third-button, r792
Commit contains DLL: No
Revision comment:
Related to issue #202: Updated docs to use correct casing of Tooltip.
Related to issue #355: Changed GUI:Play to GUI:PlayMission.
Related to issue #1215: Updated docs to mention uimd.ini.
Any updates on this? Simply curious.