Version: 2.3.1 (using KDE 4.4.5)
I connected my phone in "Media player" mode > MTP protocol is used (instead of Mass Storage Device)
Moving and deleting files works properly if the format is MP3, but it seems MP4 or M4A is not supported. I can understand this. But the message shown is "Songs are currently already present on the device" ("Pistes non copiés : les pistes sont déjà présentes sur le périphérique." in French), and it is false...
Show an message "Format not supported" if the format is effectively not supported...
OS: Linux (x86_64) release 2.6.34-ARCH
*** This bug has been marked as a duplicate of bug 234876 ***