after third typed letter java script shows up instead of terms

I use the 6.9 drupal with its included taxonomy module.
I enabled one vocabulary for one node type.
If I type one or two letters everything works (see first screen shot).
When I type a third letter I see a very long list of source code, presumably java script I think (see second screen shot).
This happens with current Firefox and IE7, so it might not a layout or browser problem.
If anyone would gibe it a try:
http://lobaloma.de/
and then create a new content object "eigenlob".