So I've been noticing that skills I have morphed are not leveling correctly. Or they gain XP correctly until I level another skill in the same tree. When I level another skill in the tree I literally see one of the other skills XP bars decrease.

This is on my Nightblade character and here is the exact situation I noticed. I have noticed this loss of XP several times, but here is the most recent example.

I had some skill points to spend. I was perusing my options and finally decided that I wanted to increase a passive in my assassination tree. I applied a skill point to the "master assassin" skill and then when I scrolled up I saw "killer blade I" losing XP. Literally saw the XP bar decrease by about 10-15%.

I have seen it a couple times, but it happened the same way again in the shadow tree which made me realize exactly what happened. So basically the same thing, I put a skill point in "Refreshing Shadows" and my "Concealed Weapon I" XP bar decreased by about 10-15%.

So I don't know if this issue is just with leveling passives, but next time I will record it and post a video if you can not reproduce the bug.