UO Second Age

I have counted the seconds and this appears to be random, and only happens to me on my dexer temp who uses offensive magery. I will precast ebolt or explosion while in combat, swing a couple or a few times, unequip, try to cast and the target disappears but I cast nothing. This has happened to be dozens of times so I wanted to bring it here and see what's what. Hold long can you hold a spell for so I can prove or disprove this?

30 seconds

If this is happening on a dexer, my guess is you're using a bandage-self macro while holding the spell, which cancels the spell, but keeps the target cursor up.