Thanks for the report, fixed for next build.
FYI the expression "64?OffsetX=0:OffsetX=64" reads as:
1. Is 64 not equal to 0?
2. If so, return 1 if OffsetX equals 0 else return 0.
3. If not, return 1 if OffsetX equals 64, else return 0.
This is nonsense and can be simply written "OffsetX=0". Still, the weird expression uncovered a bug which has been fixed, so it's fine I suppose :)