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.
Regards,
Surbhi Maheshwari