https://bugs.freedesktop.org/show_bug.cgi?id=110214
--- Comment #57 from Diego Viola diego.viola@gmail.com --- I contacted Thomas Dickey (maintainer of xterm) and he said this about the issue:
drivers, or Xorg in general -
for instance the parts painting by XCopyArea (used by xterm and some other applications) may not be getting repainting-events
https://lists.cairographics.org/archives/cairo/2015-May/026284.html
or buggy acceleration features
https://invisible-island.net/xterm/xterm.faq.html#compiz_bugs