I can confirm it's a bug, but it's kind of a corner case, and this is #1 for the procedure you've followed:
"Make sure that the drive or drives you are removing have been removed from any inclusions or exclusions for all shares, including in the global share settings. Shares should be changed from the default of "All" to "Include". This include list should contain only the drives that will be retained."
So as long as the instructions are followed there won't be a problem.