Observation:

We noticed, that when Qt is being used as part of an AudioUnit plugin (dynamic library built with static Qt) and hosted into Apple's Logic Pro (which uses so called "out of process hosting", creating a sort of remote executable to run the plugin), the cursors cannot be changed.

Notes:

When looking into the implementation, it seems that changing the cursor itself does work (using [NSCursor set]), so the source of the issue seems to come from somewhere else, possibly from how cursor invalidation is done. E.g. the cursor is only changed once (if the shape changes), but afterwards not anymore. This does not seem to be enough to "stick" in this situation. Another explanation for the issue could be, that there is an automatic reset to the arrow cursor happening at some place for some reason.