As far as I understand here the only "irregularity" present is the accent of 1st. p. sing. not being at the end.
Let's me explain.
колебáться I if its stem is
1) колеба- (as резать) then would be колеблý, -ёшь, -ёт ; or moving the accent from the 2nd person: колéблешь, ...
2) колебай- (as делать) then would be колебай-у, колебá/ю, -ешь, -ет
So being, as it is, the stem колеба- the only "irregularity" that I see is колéблy instead of колеблý.

Ready to accept stones on my head