i was mistaken about the SpecialIdle.kf fixing the idle pose for me... somehow i must have messed up something. In fact i'm not able to reproduce the initial problem, that the idle pose won't play at all. However, I've played around with the files a bit, and realized, that at least the bug with the idle animation getting interrupted from time to time, is actually another idle, but not this mysterious specialidle.kf i mentioned in the comment above, but rather the stand1.kf.
So all i had to do to fix it was opening the idle.kf included in this mod with nifScope and changing the value for "0 NiControllerSequence" from "idle" to "SpecialIdle_Stand1". Its the first entry in the BlockList (View/Block List, or F2) and simply double clicking the value field makes it editable. Make sure the Cycle Type of the "0 NiControllerSequence" is set to CYCLE_CLAMP (again, editable through double clicking the value field) and save it as stand1.kf in the _male|IdleAnims folder. That's all.
I'm sorry if i've confused someone by blabbering about blender, and moving a root bone, that could be possibly neccessary when exporting the idle animation with it only...
So at least the bug with the default stand sometimes playing i could fix for me.