When you smart cut (⌘ ⇧ X) or smart insert (⌘ ⇧ I) the program deselects.
Design Rationale:
For a normal Cut (⌘ X) operation it makes kinda sense to automatically deselect as it's unlikely that any selection-specific action follows.
1) If you wanted to do a color-bucket, you could have simply just filled over the selection, no need to first delete it.
2) And anything else: Very unlikly as all pixels were cleared.
But for smart cut it is possible that you want to continue with the selection with any of the following scenarios:
1) Either just trigger another smart cut or 2 or 3… with the same dimension, not intended for pasting but to dispose off. "Cut out a column. Hmm. Another column. Hmm. One more."
2) You want to manipulate the new content which slid in (from right of the column, or below the row). A possibility which is not given normal cut. But very well makes sense for smart cut. I.e. apply a filter or tinting right away on a selection of the same size.
And for Smart Insert the rationale is simple: Insert a little more… A little more... a little more… (with whatever content filling method chosen)