Not sure if intentional or not). Tested with 2 diamond swords (both rare).

The problem is occurs with the better combat mod, which allows you to swing with each arm. I'll also report with them, but I think that's the missing link between my report and your findings.

Hmm I know why this isn't working - I'll look into a fix for it. Alongside that I'll probably also be looking to further integrating both the new 1.9 features and Levels more.

I'm closing this for now because I can't seem to find an issue with it. Just comment if something is still wrong.