Platform, device version and operating system
At least Android & Steam
What you were expecting to happen, and what actually happened
When Psion matches skulls versus Diviner, Diviner keeps its Mana and Psion does not get any via his Siphon-Trait. I expected the trait to work because Diviner is only immune to Mana Drain, not Mana Steal.
(I expected immunity to Mana Steal to be an advantage of Mana shield over Sky Ancestry, but currently Sky Ancestry comprises all of the Mana shield functions + immunity to silence and faerie fire)
How often does this happen? When did it begin happening?