#3 drawing-error

[Piotr Sawuk]

the most severe bug is that after altering the
bit-field and stepping forward one gets unexpected
results, stepping back again does reveal a bit
being set which was not visible while editing.

this only happens rarely, and only when the
animation has been traced back and altered
several times.

I suspect this is related to the fact that (at
least in my case) the drawn point is slightly
below the pointy end of the arrow-cursor,
although this bug only seems to happen in
the upper right corner of the altered area.