[plt-scheme] Graphics

For some reason, using my memory-canvas%, when I draw a lot of bitmaps 
sometimes (most of the time) only some of them show up.
It is unconsisted
I attached a zip of 2 examples of bad behaviour and one of correct 
behaviour.

Would you happen to know what could be wrong?



Note #1: these are lowest-quality jpegs with 256 colors, thus they take 
only 2689 bytes accumulated, to reduce mail download time.
Thus, they look *awful*, but you can still make out that in error #1 
there are missing lines and that error #2 has those drawings missing.

Note #2: The lines are also bitmaps.


Thanks,
Katsmall the Wise
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