Weird - I really don't see how this is possible....

So, I jailbroke my 3GS about a fortnight ago so I could upgrade from 4.3 to 5.0 (9A334) from an ipsw GM from IMZDL. All has gone well in the intervening time - stable, rarely a crash, and I only got caught out once away from my computer when I needed to tether boot. 
What is weird is that while I was in London this weekend, it crashed to a black screen with a spinning ‘wait’ icon. It was like this for about 3-4 mins, so I assumed it was stuck, and I powered it down. Out of curiosity, I powered it back up again a bit later, and my wee iPhone powered and booted up to the lock screen, and to a completely functional phone. I have spent that last few days trying to make it need a tethered boot, but thus far, it keeps acting ‘normal’ and booting straight through. My Apple TV is certainly >not< this compliant, and needs me to wander over the other side of my sitting room each and every time it bombs; but not my phone. I understand the untethered JB isn’t due for a bit yet - so what the farming hell it my phone up to? Not complaining…I just don’t understand it - like really…

Any thoughts would be welcome, and as a final note, I have installed nothing knowingly like same-tethers etc to make this happen…it is a vanilla Seas0npass 7.9 creation…

Cheers - Dunc