Hey so I found this today when logging in. And I could only recreate it logging in freshly after doing it the first time.
Step 1. Have an item you want to equip (I tried a 52 cloak at lvl 51 called the Chancellors cloak - missed ss's but ill post ss of a 1h mace on a Necro). We will refer to this item as the "bugged" item
Step 2. Have 2 other items that actually go into the slot u want the "bugged" item to into. (Equip 1 of these items and leave the other in your inven)
Step 3. Drag the "bugged" item with your mouse button over one of the 2 non bugged items (you should be hovering over the one in your inventory). If you are correcly holding the "bugged" item over the non bugged item you should be holding down the left mouse continuously
Step 4. Now with the item hovering over quickly spam right click and let go of the left mouse button after you see that the 2 non bugged items have swapped places a couple times.
Step 5. Bugged item now in said slot but as for removing it - that is a little tricky and I had to manually drag the bugged item out and replace it with a non bugged.
*edit* it seems to reset on a relog too.
http://i26.tinypic.com/hwis7a.jpg - thats a 1h mace - stupefying mace on a necro and the mammoth on chest ....
As I posted below I tried it with a belt that added 223.5 max hp (1479 self buffed with some food in the pic):
http://i32.tinypic.com/1z56m4h.jpg
then with the belt on adding +223.5 hp I went up to 1703 approx 223.5 rounded (1702.5):
http://i25.tinypic.com/b533b5.jpg