Hireling Auras changing in NM

I hired a prayer merc in normal, when when I got to nightmare, and looked at my hirelings advanced stats, his prayer aura was replaced with thorns. Just to confirm this happened, I switched back to normal with the same char, and indeed, my hirelings aura was now prayer.

This is very inconvenient because it means that a might aura hireling from nightmare, will have blessed aim aura in hell.

This is not a change that is listed on the list of changes to the game, so I assume it is a bug.

This is happening to me as well. Except, I hired a Holy freeze merc from A2 and it’s currently changing to defiance when I log into Hell. It changes back to Holy freeze when in nightmare. The display of the aura is reflecting an accurate representation of the hireling’s current aura in each difficulty.