I think I found the solution myself. It seems that if the topic is open the conditional build tag will be removed if the snippet is edited. If the topic is not open it's OK. so I guess one should be careful to only have open things that one is actully working!
I don't think that should happen. If you can reliably repeat that, it should be reported.
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Thanks Peter, I will do that!
I received the following reply to my bug report:
We have fixed this issue in the later versions. In RoboHelp 11, it works fine.
In RoboHelp 9 the only workaround is to close the topic and then change the snippet, in that case the CBT will remain be applied.
Thanks again for writing to us. Feel free to query in case of any confusion.