RegexCommentHandler not saving splitregex property in JIRA 5.0

I created a mail handler of the type "Add a comment before a specified marker or separator in the email body" and I set a splitregex and saved it, but the splitregex parameter doesn't get saved to the properties table (the propertystring table)

The other properties do save, and if I click 'Edit' on the newly created mail handler, its 'Split Regex' field is blank.

To debug this, I went into the database and added splitregex=/_____+/ to my handler params, then restarted JIRA and sent a test email and verified that it works as expected (so I don't think anything is wrong with the RegexCommentHandler class itself, just something not saving properly with the properties edit panel so the splitregex field isn't making it into the properties.