I've got an LG Nexus 5 and a 2012 Nexus 7 with 4.4.2, and the round images work fine on both.
The fix I just added is specific to 4.1-4.2 inclusive.
Can you try this:
In AquaMail, go to settings -> debug -> disable GPU. Exit AquaMail with Back, restart, check if it fixes it for you.