I've looked through it. Your inheritance tree is sort of messy, which is probably what causes issues. You need to make sure that the groups inherit from each other to make sure that the "ranks" are setup in the right way (I also just noticed that you said superadmin doesn't inherit). A lot of groups inherit from a group that inherits from user. For example superadmin. It should, in theory work, if this is done:
user - can_target: !%moderator
moderator - can_target: !%admin - inherits: user
admin - can_target: !%senioradmin - inherits: moderator
senioradmin - can_target: !%supervisor - inherits: admin
supervisor - can_target: !%superadmin - inherits: senioradmin
superadmin - can_target: * - inherits: supervisor
The last part is the most important one, since if superadmin inherits nothing, it inherits user by default (at least I think so), which in the end means that it's pretty much not anything higher than moderator (that is rank-wise, command-wise it's different).
I hope I explained it right, since this sort of confuses me too (to anyone: feel free to correct any mistakes).
You should read these for a better explanation:
"How exactly does can_target work?" by Stickly Man! -
http://forums.ulyssesmod.net/index.php/topic,5346.0.html"Immunity: How It Works Now" by atomicspark -
http://forums.ulyssesmod.net/index.php/topic,4314.msg16844.html (I recommend taking a look at the first reply in this thread too, by Megiddo)