Lipo at 2.6V?

[What's_nitro?]

I would do a couple of C/D cycles on the bench and see how that cell behaves. Over-discharging doesn't put you in danger of a LiPo fire, but it can damage the cell irreparably.

As far as the MM goes, the Auto-LiPo will only detect the number of cells properly if you hook up a fully charged pack. The cell in question may have dropped voltage very quickly after coming off of the charger and caused the MM to detect 5, instead of 6, cells. With the pack fully charged, do you hear 6 beeps when you turn on the MM?