4.0.0.12 was the second early adopter release - a beta, in other words - and was released in September 2013. There was a third EA release, and there have been three production releases so far since December.
The current version at the time of writing is 4.0.2 (4.0.2.15). Unless you have a pressing reason to stick to the early adopter/beta version you should probably just upgrade to the production version.
I can't immediately see anything relevant on the SQL Developer forum, which is where early adopter issues were supposed to be reported. That doesn't mean it wasn't reported, or spotted internally, and fixed. I doubt they'd be very interested in this now if it has already been fixed in a later version, though.
If you upgrade and do still see this or any other bugs then the release notes say to report them on My Oracle Support.