When I am rejecting a suggested edit, I like to use the "custom" box to give more directed feedback to would-be editors. But there's a minor usability problem there that disrupts my workflow.
After I've finished typing and press the Enter key, I expect the form to be automatically submitted just as if I'd moved my mouse down to click the "Reject" button.
Instead, the Enter key currently returns to a new line, which is useless considering that the suggested edit rejection reasons don't show line breaks.
I realize that the standard behavior of the Enter key is to insert a new line, but having it trigger a submission for something that doesn't support multiple paragraphs is not unprecedented. We do precisely this for the comment box already. You have to press Shift+Enter in order to return to the next line. The "custom" field in the suggested edit rejection dialog should work the same way.
With the suggested edit queue regularly overflowing, anything that helps the users slogging their way through the seemingly infinite list of edits do so more efficiently seems like a good idea to me.