Hrimnor's Hymn Aftershock bug

Not sure if this is a bug or by design, but this is what I am experiencing when using this item on my titan:

The guaranteed aftershock from this unique overrides the aftershock chance from other sources besides Seismic cry. As an example, I am using stampede, earthquake and hammer of the gods. I have Split the earth notable plus the small passive for 18% aftershock chance. 25% from the aftershock support gem and 20% from the Titan ascendency for a total of 63% chance of aftershock. When combined with Seismic cry I have one guaranteed aftershock and of course I see a second aftershock about 63% of the time. When using Hrimors's Hymn with the same setup, I always get 2 aftershocks with Seismic cry but NEVER 3. So, the 63% chance for an aftershock is disregarded when using Hrimnor's.

Thanks for reading and your consideration.