PHP will fail to return a filename when the file has utf8 characters in it.

[SeanJA]

If you are using a version that returns the actual file name submitted instead of a randomly generated filename, you will run into problems if a user submits a file with the name (for example) ÎOâÂ¥.jpeg as json_encode will return null instead of the expected \u00ceO\u00e2\u00c2\u00a5.jpeg.

[dresende]

I never had any problem using utf-8 characters...

[SeanJA]

This problem seems to have gone away in later releases (not sure why...?). This can be closed.