The subrace skin system is not working correctly: The subrace skin will be re-equipped upon login and thus some stat settings are reset. (Thanks to Riverwind for pointing this out!)
And if finally found the reason for it! Quote nwn.wikia:
"Player characters (PCs) can be given skin items, but players cannot equip these items through the radial menu like most items — that must be accomplished through scripting or the quickbar (usually through scripting). Furthermore, a PC's skin item will be destroyed upon entering a server if the server has either item level restrictions or enforce legal characters turned on. ..."
Until we found a way to preserve these stat adjustments, you'll have to re-adjust some settings on your toon (eg. an additional spell slot) manually on each entry, because the subrace skin will be re-added and re-equipped. SORRY for the inconvenience.