Apparently, it _was_ related - both the error messages and the problem seem to have been caused by the use of glColor4f(). I've replaced it to a call to StelPainter::setColor() with the same parameters and it seems to work the same, but without the errors.
Apparently, it _was_ related - both the error messages and the problem seem to have been caused by the use of glColor4f(). I've replaced it to a call to StelPainter: :setColor( ) with the same parameters and it seems to work the same, but without the errors.