Radio button in Wordpress' update page saved wrongly

On a Wordpress installation that doesn't have write rights to its files, Wordpress falls back to an FTP implementation. You have to enter all credentials and also have to select whether you want to use FTP or FTPS to connect to the server.

This selection is done through a radio button group but 1Password doesn't save its value correctly when it creates an entry after I clicked "Proceed".

I checked the result of "Copy JSON" and it says:

{"value":"ftp","id":"ftp;opid=__3","name":"connection_type","type":"R"}

Here's a screenshot of the form together with its HTML structure:

I'm running 1Password 5
Version 5.3 (530032)
Agile Web Store

and Firefox 37.0.2 on OS X 10.10.3.

I already disabled "Animate form filling" (as stated somewhere else) and also tried to manually create the entry in 1Password (through the browser extension) before clicking on "Proceed". Neither approach did solve the problem.