That's strange that it stays on after a twist, I'm not sure if the tapping you did somehow jarred the last bit of emitter off the filament.

I think it might have been some dirt (part of the phosphor,...) covering the last working part of the filament and when you twisted the lamp, it fell off, exposing the working part to the gas...
But the lamp would die soon anyway, i guess, so have the replacement tube and starter (the old one would be worn out by this long flashing) ready...