If you believe you have found a bug in ArchiCAD that would be difficult for our team to reproduce it may need reported to Graphisoft.
One of the most useful things a customer can provide is a ‘support package’ of the file which will contain a lot of information about the project without storing the project data itself, so your not distributing your file but providing all the necessary information for Graphisoft to discover what the issue is.
You can create one by going to Help>Create Support Package. There are various options you can choose based on what you need to send (solo or teamwork etc)
Further information about Support Packages can be found here: http://www.archicadwiki.com/SupportPackage