gitk error on checkout of branch

Hi,

using gitk (git 1.8.3), the program gets stuck when checking out a new branch if the last checked-out branch was the bottom left branch. The error occurs consistently in this repository, but unfortunately, I cannot reproduce the error on another repository. The message reads:

invalid command name ".bleft.bottom.ctext"
    while executing
"$ctext conf -state normal"
    (procedure "getblobdiffline" line 10)
    invoked from within
"getblobdiffline file6 5f7f5bd07fb3de12ce64dee4f19e060c9d62cc54"
    ("eval" body line 1)
    invoked from within
"eval $script"
    (procedure "dorunq" line 11)
    invoked from within
"dorunq"
    ("after" script)

any suggestions on what to do are appreciated.

kind regards, Steven