The edit summary is appended with a whitespace character in the user profile's revision list.
When I've needed to copy-paste an edit summary I've ended up taking the extra work to not select the whitespace. But later I realised that entering a trailing whitespace in the edit summary causes it to be trimmed and it's only shown in the user's revision list and in the post timeline.
Unless there's some practical need to keep the whitespace I think it should be removed because text selection is more accurate without the trailing whitespace and it would minimize potential confusion for the user.
Also interesting to note that in the edit history of a post system generated edit summaries don't have the trailing whitespace only user entered edit summaries have the whitespace.