in AutoCreate screen, can't return all PR in one step.

in my autocreate screen, I want to return all PR to requester. So I select all Requsitions and click on "Tools>>Return Requsition". But without any error message, some of them are still on autocrete. I do the same, some of them return and other is still on screen. Then the same thing.

I want to learn why I can not return all PR in one step.

The only difference is some PR's line are already converted PO. But still on autocreate screen which I see that PR, I wanted to return. I can return them step by step. why?