Update: Here's the response from earlier this morning:
> Thank you for taking the time to write to us here at AgileBits. The current version of the 1Password extension does not use regex to parse URLs for this exact reason. We don't autofill either, which also helps avoid issues like the one you mentioned.
I have sent a message to 1Password through the official customer support channel to ask the same question posed here. I'll update once they reply.