[BUG] gitk: fails while unfolding dir in tree-view

When using the "tree" view and trying to unfold a particular dir, I got
the following error:

can't read "treeheight(lib/)": no such element in array
can't read "treeheight(lib/)": no such element in array
    (reading value of variable to increment)
    invoked from within
"incr treeheight($x) $n"
    (procedure "treeopendir" line 15)
    invoked from within
"treeopendir $w $e"
    (procedure "treeclick" line 20)
    invoked from within
"treeclick .ctop.cdet.right.cfiles 18 233"
    (command bound to event)

This occurs with 1.4.3.3 as well as current master.  The tree exhibiting
the problem is from http://git.debian.org/git/deps/deps.git - select any
revision, switch to tree view, and attempt to unfold "lib" (the last
entry in the list).

Best regards,
-- 
Yann.