I also have some patches in the area of new handling but have been too busy recently to deliver them, but will submit a PR in the next few days. There are a few parts to the puzzle. The xmltv "new" (mostly) doesn't mean "new episode", and Tvheadend's checking for new is "new or unknown" and so relies on "not identifiable as a repeat", which isn't necessarily the same as new.
What grabber are you using? IMO, your xmltv should have premiere if it is a first showing, though other people have altered their grabbers to implement other behaviour such as suppressing previously shown ("repeat") tags.
And, as Robert says, there seems to be a problem sometimes with EPG updates. The epgdb.v2 is in ~hts/.hts/tvheadend/ directory on a normal distribution.