gitk: git bisect view doesn't work

gitk bails out like this if I do "git bisect view":

$ git bisect start HEAD HEAD~2
Bisecting: 0 revisions left to test after this
[9a61060c7e0d112d0742f5b845210ea8c41b6c6b] Added encoding

$ git bisect view
Error in startup script: can't read "notflag": no such variable
    while executing
"expr {!$notflag}"
    ("--not" arm line 2)
    invoked from within
"switch -glob -- $arg {
            "-d" -
            "--date-order" {
                set vdatemode($n) 1
                # remove from origargs in case we hit an unknown option
                set origarg..."
    (procedure "parseviewargs" line 21)
    invoked from within
"parseviewargs $view $args"
    (procedure "start_rev_list" line 27)
    invoked from within
"start_rev_list $curview"
    (procedure "getcommits" line 5)
    invoked from within
"getcommits {}"
    (file "/usr/local/bin/gitk" line 10897)

$ git version git version 1.6.1.rc1

-- Hannes