after upgrade to latest version

UI version: 7.8.1 Rev11
Server version: 7.8.1-Rev12

within calendar month view there are no entries visible between april 16 and july 16. All entries are visible in day/week etc. view - that means they are there, but in month view not visible. Even if i create a new entry e.g. on 4th of april 2016 it is not visible in month view. If i create an entry on e.g. 27th of march everything is fine.

More interesting is, that this happens only in english gui. Setting language to DE or HU everything seems to be ok and calendar entries are visible also in month view.

Workaroung: use DE language/gui until a solution :-)

Any ideas or a solution?