The following test fails (It works in 2.8.1.final):
groupBy throws an exception in 2.9.0 but in 220.127.116.11 just returns the wrong value.
Essentially what is happening is the groups are formed correctly but the values in each group are always the entire collection. I believe the bug is in TraversableViewLike:170. Look at the implementation:
The section newForced(thisSeq) probably should be newForced(xs).
I have tried this in a subclass and the fix worked.