Sony Walkman Phone Problems

Does anyone else have one (the Sony Eriksson W800i Walkman phone) and has anyone else had any problems with it?

Basically I'm copying MP3's onto a memory stick via a USB1 connection either through file manager or sony's own Disk to phone software.
I can see the files on the memory stick when its connected to the PC, however when I disconnect and use the phone, I can only see a portion of the MP3's I ripped onto it (eg 10 mp3's ripped, can only see 2), and then when I reconnect the phone to the pc I can only see the files that I could see via the phone.

Has anyone else had this problem (either with the phone or other MP3/Memory Stick devices)