I've been using x3 for couple of days and found 1 serious bug in the latest firmware.
Occasionally, when playing musics (standard MP3 files) following sequence of button manipulation triggers freezing of the device:
1. While playing - Press Play/Pause button to stop playing
2. Press Bookmark/Back button to return to list
3. About for 10% of probability (rough estimation), the screen only shows background image except top information line part (track number, volume, play mode, battery status)
4. The device doesn't respond to any button manipulations, except Reset button.
5. The device can be restarted by repeated 'Reset - multiple click of Play button' combination.
I hope this is firmware related issue and can be fixed in the next update.
Thank you for reading.