A GC-icon display is implemented with a child window on OS X. In some
OS X version prior to 10.10 (not sure which ones), screen
reconfigurations did not move child windows properly relative to
parent windows, so all child windows were reset after a screen change.
In 10.10, meanwhile, Mission Control can cause screen-change
notifications, and adding a child window to a Mission
Control-minimized fullscreened window will goes terribly wrong.
Fortunately, 10.10 seems to update child-window locations correctly on
screen reconfigurations, in which case the old workaround that hits
the new bug can be skipped.
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