I also have been having this issue..I have been trying to figure it out for 3 days and what I've found out is the following for my situation..
1.) When I played in windowed mode had no problems...
2.) Once I went back to full screen the same problem..
3.) Today I went into appdata world of tanks and deleted the preferences file and everything else in the folder restarted game and played in full screen perfectly for 2 hours reinstall the mod pack and again same problem..