Cursor is either empty or garbage when compiled against macOS 10.13 SDK
It doesn't happen when an older SDK is used, hence I suggest some OpenGL bug has been fixed by 10.13 and its workaround is still in OSG and is causing this. It doesn't happen when an OpenMW build compiled against SDK < 10.13 is run on macOS 10.13 (i.e. all releases & nightlies to this date are not affected). It apparently happens because Apple is known to guard breaking fixes by so-called link version checks, i.e. fix comes in effect if and only if (for example) a binary is compiled against 10.13 SDK or higher.
Unfortunately, I couldn't find any official macOS 10.13 OpenGL bug fixes list, thus it might as well be just a bug that is somehow triggered by the linked SDK version.
It looks like the following code fragment is problematic: https://github.com/OpenMW/osg/blob/2b4c8e37268e595b82da4b9aadd5507852569b87/src/osg/Geometry.cpp#L745-L755 because "Warning: detected OpenGL error 'invalid framebuffer operation' at end of Geometry::drawImplementation()." gets printed if GL error checking is enabled in sdlcursormanager.cpp.
Respective forum topic: https://forum.openmw.org/viewtopic.php?f=8&t=4829
(RM-4424 from redmine: created on 2018-05-24 by Nikolay Kasyanov, )