I am surprised that so many posters are so lenient regarding this issue.
I do prefer the flaps to be quite tight for myself(given appropriate shoe, etc., of course).
But there is some wiggle room while still being proper and I think the example shown by the MoL is a good one of such.
However, Willin, if your shoe spreads like the image in your OP, especially the left, I just have to say I think it is ugly business.
Less of an issue if you are wearing a very casual outfit but, honestly, it still bothers me when it is so extreme.
Also, when it appears the gap is due to an ill fitting shoe rather than by choice, that is the truly objectionable case.