Battlemage's Increased Duration passive is bugged. Instead of adding 1.5s per rank to Prismatic Barrier's base duration, it adds 2% of a second per rank. At max level, Prismatic Barrier goes from 30s to 30.1s.
I only have 3 Ascended characters, so I've only been able to confirm that the Juggernaut and Marksman versions of that same passive are working correctly.