Thank you.
I just tried with a PRS-650 and latest nightly form the default-repository (it is near but not identical to ZORK), and I found no problem.
Though it was reported before, and there might be a problem with "highligthing" see
issue 342 on the project-page.
Maybe it interferes with some of the Tap- and/or Swipe-Options.
Try to reset them all to default.