gitk dev branch: F5 gives error after commit

I use the dev branch of gitk (on Windows), commit 476ca63 (gitk: Index
[fnvr]highlights by id rather than row).

1. Start it with:

    gitk --all -300

2. Make a commit.
3. Hit F5. Here I see the error message:

   Error reading commits:
   fatal: bad revision '^-300'

At this time the label of the current branch is already gone from the
commit list. There are no other changes made in the display.

Hitting F5 again does nothing. I have to create a new view to get an
updated display.

Any help is appreciated. Thanks,
-- Hannes