Nothing to worry about, it just happens every now and then. Sometimes it happens twice in a week, then there's no problem for months. Nobody ever figured out the exact reason.
I got the PS2 tonight, I played with it for a while installing FW34v2. A while later I booted up the PS2 again and it seems like the Firmware was gone. It just booted into the normal PS2 menu. I powered it off fully and checked again. Same thing. Once I reinstalled the Firmware (not BM) it worked fine again. Should I worry about this? I don't want to have to reflash the FW once-a-day!
Check the wiki, there's a bit of documentation about PBAT and you should be able to get the rest by learning and doing.
I'm looking forward to playing with this anyway, and learning the BM PBAT syntax. Such a shame such a great chip is no longer developed, I wish they'd just release the BM source.