Coming back down a dark cloud street over a mountain valley I pulled into a

vigorous thermal at 50 kt.

Some 270° in the first turn I was flipped inverted and spat out on a
downline in
an eye blink. The trace showed an 11kt drop in TAS in one second followed
by a
9 kt increase one second later.

Best to get the stick back before the airspeed builds recovering from
inverted.

While many glider manuals allow loops, there's very few that allow rolls.