If you have shadowguard (troll racial ability) active you will take damage when you heal yourself

After some testing, I guess this applies only if you have the shadow weaving talent in the shadow tree.

Basically a full rundown:

1) You have shadowguard active.

2) You have shadow weaving talent.

3) You cast heal on yourself.

4) You will get shadow vulnerability on yourself and take damage from shadowguard.

Nothing after 3 should happen obviously.