Hey topher007
I'm sorry to say we're aware of this outstanding issue, and it doesn't sound like it is going to be something either quick or easy to fix. At the moment the best workarounds I could offer would be drag & drop from 1Password into the field, or as you've found, a second Login item. Ideally we'd like to be able to support custom password fields in the future but there is some major work that would need to be done to our filling "brain" in order to accommodate that, and it isn't on the radar at this time.
Ben
ref: dev/core/core#3493