NeutrinoRDP:bitmap overlapps when using painter

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version:v0.9.21.1
compile options:all default

When I pan a window in remote desktop, the bitmap overlaps.
like this:

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Only bitmap updates. Orders are ok.

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I follow the code in xrdp_mm.c:

And log for wm->screen and wm->target_surface and found them are the same bitmap.
When I make a copy of wm->screen and replace it. Everything is OK.
Maybe memory overlaps ?

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It can be reproduced when using freerdp stable-2.0 (which gdi is disabled by default) and above to connect.