Didn't someone tell me this would not be the case?

If you are incapacitated and return to base camp without being revived, or if you leave the instance while incapacitated, you will lose a portion of your knowledge. Should your knowledge fall below zero, your knowledge level will also decrease. The amount of knowledge lost depends on your current knowledge level.
Anyway, that's OC for me - I just can't stand this sort of garbage mechanic.