If 'Eigenes Dialogfeld' means "show custom dialog", see: Known Buglist for Filemaker GO
This is one of many acknowledged bugs that can be found in the Known Buglist for Filemaker GO here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Thanks for your kind words. Unfortunately I'm not aware of the english syntax - I added 'custom dialog' after writing the post If You think that foreign users should not report bugs here, that's OK for me
Please do report bugs. Many FM GO bugs are reported here, though you are actually expected to report them in the Report an Issue Forum where there is a form that pops up for collecting detailed information about the issue that you are reporting. In this case, I was guessing that this is an issue just acknowledged this week by FileMaker Inc. and I was providing a link to that thread so that you had access to the latest information and could confirm that I was guessing correctly.
The Known Bugs List is something I maintain here in the forum to make researching possible bugs a little easier as you can search this list to see if the bug has already been reported and acknowledged by Filemaker Inc. You can also use this list to check the current status of each such acknowledged bug and sometimes find workarounds to help you deal with them.