Well I'm seeing exactly the same issue in Book II - sometimes my Fighter is able to cast Gravedigger's Flame or Cat's Eyes or Bless or whatnot while still holding his sword with gloves, but sometimes (esp. in combat) he can't and so I have to switch over to my second Weapons set (with just a pine Club) in order to spellcast.
Anyway, if that weren't bad enough, it would also seem that the "1/3 of strength = somatic weight" requirement is either buggy (or purposely rounds up!) - my Fighter is STR=20; the weight in my hands (i.e. gloves + sword) is, total, 6.5 pounds (or was up until about 5 minutes ago!


Anyway, anyone else seeing either of these issues?...