All billboards have disappeared

[Lewk]

Exactly what the title says. In the regular game, none of the billboards are visible. It doesn't really bother me much, I'm just curious if anyone else has/had this problem.

EDIT: just to clarify, all the billboards in custom stories and such still work. It's just in the actual game levels. Also, the billboards aren't even visible in the level editor of the games levels either, which makes it more odd.