When you clone one volume to another, the index for that volume is also cloned. If you disable indexing for a destination volume and then create a clone of a volume on which indexing is enabled, the clone will also have indexing enabled. If the destination volume is erased during the cloning process, then it is immediately available for Spotlight to begin indexing again.

This is not a bug with Spotless; rather a problem with the way the various cloning applications handle Spotlight indexes.