Yeah, that's pretty much it.
I just experience the same bug for the THIRD time today. It actually does not necessarily need to be all locked as I found today (the first two times just happen to be all locked ones that dropped and came together). It just happens when you have one available move left, and the followings that drops down won't remove even if it were the same colors.
I guess it will be easier if I illustrate it:
for spinned 3gs drops 3rs moved yup!
example g g b removed down stays on dead!
r r r
g b b
g g
b g b "locks" "bonus" -FREEZE-
g g r
r r r r
r r r r
And this only happens in "Survival mode" as I mentioned