gitk - fails to highlight commits

Using gitk on master (281404ca1db4c921ac162f3c0 in the gitk) gitk's 
highlighting is sporadic. Running gitk from a gitk sandbox and typing 
'gitk' into the 'Highlight Commits' box shows nothing highlighted, but 
all commits should be highlighted. After doing this, many of the commits 
revealed by scrolling down the list are highlighted, just not the ones 
visisble at the top nor the first few below.

This problem first appears in commit 322a8cc ("gitk: New algorithm for 
drawing the graph lines).

Mark