I recently came back to UO and decided to play a mage. After I reached gm magery I got my hands on a 110 SoP. After around 1200 casts of EQ I went from 100 to 103.6, which I thought was painfully slow. So I was looking for more optimal ways to gain. I've read on uoguide.com that a -29 magery wand or similar mage weapon would reduce your skill and help you gain a bit easier so I decided to try that. Now here's where the oddity occured.
I had only recently placed a vendor on my porch and put all the crap on it from the past few days. Amongst said crap was a bag of weapons, with a -26 mage skill scimitar. Remembering this I went to the vendor, opened his goods and dragged it straight from the vendor's bag to my paperdoll.
Don't know why but I went from 103.6 to 110.0, and the weapon got bumped back into the vendor's backpack. I waited a few hours, logged out a few times to see if the gain was permanent or not and on first notice it is.

I don't know if a server reset will remove the gain, I'll edit this thread if it does.
Will try to get my hands on a 120 magery SoP meanwhile and see if I can replicate the previous.
UPDATE: I found a 115 magery SoP, but as soon as I used it it reverted my skill back to 103.6. However upon using the trick explained above it jumped to 115.0 and sticks there. I'm guessing a server reset would revert you back, I'll have to wait and see to give closure. Still, a nice bonus until then!