I got it to reproduce and I think it's related to the updating of the info screen, which you probably haven't been doing, and I do at the beginning of every game.
This is the save - http://dl.dropbox.com/u/16872572/nequipment%20bug.EleSav
At the beginning of every game, once I get a horse, I edit the info cards of every champ because the game does not save the info cards. I keep the horses equipped but save the cards with the horse unequipped. The game starts out with the portraits having the horses equipped, like this
or like this, in the original state that the champion was found in.
Here are the steps to reproduce the bug.
1. Edit the info cards of everyone, except Savage Striker since he is a duplicate of Mapret and his card will automatically update. I've tried just update Rilis (since we will be using her later) and that has worked also, but I've only done that once so don't know if it works every time.
a. unequip the horse
b. edit info card, pick a pose and save it
c. equip the horse
d. the horse should be unequipped in the strip on the bottom but equipped in the equipment window.
e. Repeat a - c for each champ or you could just try it for Rilis.
If you don't do step 1, the equipment bug does not appear, at least not following the steps below.
The champions pics should look like this - (or whatever pose you chose)
2. Have Rilis buy a battle axe at the shop. DO NOT EQUIP the battle axe. This is not something I do during the game but have found it reproduces the bug quickly.
3. End the turn.
4. Equip Rilis' battle axe.
5. Now click on the Sword of Wrath. It will be highlighted, but will not equip.
Let me know if you have any questions or if I wasn't clear about something.
It would be nice if the equipment bug is related to the bug causing the info cards not being saved correctly. Then you could kill 2 bugs with one stone.
edit - This works for any champ, as long as you've done all the steps (although I don't know if equipping/unequipping the horse is necessary). Actually sometimes the horse becomes unequippable like the weapons.