I'm replaying this after some time, and have found a weird glitch. I apply the salve when the game prompts me, but the wyverns still attack. No big deal, as I can kill them, but I'd love to know why this would happen. Any ideas?

Was there a delay? It will wear off after a while.

I skipped using the salve so I could kill the wyvern (with a bow, and the odd static charge enchantment being triggered).

No, there was no delay at all; I put the salve on, headed up the spire, and immediately got attacked. I can kill them with a bow, and my creature can use magic missile and magic blast, so it's not a real problem, just that I hate it when I can't work out why something has happened.