Looks like it started happening not too long ago, I'm on the beta, and 1P mini pops up whenever I hit cmd+\ to fill in passwords.
The auto-fill works fine, but the fact that it pops up is really annoying.
1Password Version:1Password 5
Version 5.5.BETA-29 (550029)
_Extension Version: Not Provided
_Sync Type: Not Provided