when you're in edit mode, the input zone for tag is forced to height:48px; and tags go out the input field. Delete instruction in media\k2\assets\css\k2.css line 463 solves the issue

Hello and thank you for reporting this.
This has already been corrected in the repo.

github.com/getk2/k2/commit/3fccc7ae2574ef622583e513d1b6e013dd75f0c2