Un usuario dice haber solucionado sin rootear:
Guys, I might have found solution for this issue... Simple
1. Ensure that your device said internal memory full but actually its not (in my case. Thumbnail data is around 1,5 gb and after I delete it my device still said its full 100%)
2. Go to setting - Apps - all and find app named MEDIA STORAGE
3. Clear cache - force stop and disable this app
4. Activate again this app after you disable it
5. Check that you unable to play music, see the album or change your ring tones using default app but you still can access it using file explorer
6. turn off and turn on your device, you'll see that your device will do pairing with Sd and Internal in notification bar.
7. Check your storage data info, it should be back to normal
http://talk.sonymobile.com/t5/Xperia...347456/page/17