Hi, Given that updating of the calendar is deferred when the month changes (to workaround bug 2080), if there were marks (for example, a bold 3 March), the mark stays for 0.5 seconds in the new month (ie, 3 April, then disappears). This simple patch clear marks directly and avoids that phantom-effect.
Created attachment 1541 Patch against r26661
fixed in Orage 4.5.13.3 revision 26662.