Mirek,

This might only apply after release 2021.1, but I found a solution for history -- or rather the backlog of mouse events:

//				if(findarg(a.type, GDK_MOTION_NOTIFY, GDK_CONFIGURE) < 0)
				if(findarg(a.type, GDK_CONFIGURE) < 0) // *** HERE: We cannot drop GDK_MOTION_NOTIFY events
					break;
				Events.DropHead();

...

This last one dropped queued GDK_MOTION_NOTIFY events and ruined all attempts to get them through.