Adding a static counter somehow fixed the issue (for me). And then considering that something might be choking on the cpu usage in this thread, I tried a 'usleep()' which also works, and seems to be more consistent.

I am multithreading in linux. You might not have this problem.

In uppsrc/Draw/Raster.cpp I was getting seg faults ("illegal memory access") so I put a counter in the function noted below. And just adding a static counter fixed the problem.