drag and drop of a file with an illegal character just quietly fails - no error message

A customer pointed this out to me.

When a user tries to drag and drop a file with the file name containing an illegal character Confluence quietly fails and gives no error - nothing happens.

However if user tries to upload a file via 'browse' (the traditional way) then the user correctly gets this error message. Drag and drop really needs to do the same thing. This is kind of a big deal.