Olaf unit collisions in new jungle

Olaf's undertow is supposed to allow him to ignore unit collisions with neutral monsters for a short period of time. I have noticed that the debuff does not seem to be applying correctly to some of the jungle monsters, particularly the Brambleback, Blue Sentinal, and Krugs. This can significantly hurt Olaf's jungle clearing and cause him to take more damage than needed. It has even caused me to get caught in the Brambleback a few times.