Happened again. After fiddling a lot with usb hostmode, mass storage mode doesn't work anymore.

Reflashed kernel-power ver.45, still no joy. Phone doesn't react at all when connecting the usb cable.

Flashed MohammedAG kernel-power ver.40 + hostmode, now mass storage works.
Transferring files...

Reflashed again kernel-power ver.45. Again, no mass storage mode.

Reflashed stock kernel pr1.3. Mass storage works.

And now... reflashed power-kernel v.45, and... mass storage works again!

[Of course, while doing all this mess, my optfs got corrupted. Thank you, Robbiethe1st with your backupmenu].

What's going on here?

EDIT: after a while, mass storage is again kaputt. Now trying to leave the phone without its battery for ten minutes. See what happens then.
EDIT2: Geez, that worked. So, there is a cure. Good.