Has it always been the case that side xp bonus has never been rewarded when doing research? Or is this a new bug, seems strange I've never noticed this before. Maybe it's just a visual bug?
Killing a mob doing normal xp:
You received 1831772 xp.
249856 xp was gained as a side bonus!
Killing the same mob doing 100% research:
1581916 of your XP were allocated to your personal research.
Xp gained minus side xp = research gained
(1831772 - 249856) = 1581916