Found it.
https://web.archive.org/web/20030228...e=35&id=184420
It's interesting because he isn't sure and the the UI then didn't have a blue bar. If he got 1/2 a bub of exp instead of 1/3 it would have been easy to miss.
There is an 11% cap on exp events, which means the most exp you can get is 1/2 bub per exp event.
It's unfortunate we don't have any level 30+ sources. That's when gnoll scrolls stop hitting the 11% max and you can actually see the full amount of exp it gives.