Couple months ago we have detected an error occuring while uploading files with special characters in filename (e.g. München.jpg). The reason of an error could be very similar to this one: http://cutesoft.net/forums/thread/75147.aspx.
Error: http error1 :403:Forbidden
The problem above can only be reproduced with IE10 and IE11. If I change emulation mode to IE9 (IE DevTools), it works without any problem.
I have upgraded PHP from ver. 5.3 to ver. 5.4+ recently. As far as I know there were also some changes related to encoding.
Problem described above is very annoying, so please provide a bugfix ASAP.
Regards!