[ttrmw]

I've observed ZWSes appearing in user input for an application I maintain. It appears in text pasted from either Outlook or OWA, I believe. In our case, it is necessary that the application handle them gracefully - indeed, the user has no reason to know anything is amiss.

[akjainaj]

That internal server error only appears if you paste the ZWS by itself, without any valid text in the tweet at all. So yes, the user knows perfectly well what he's doing.

[rabidferret]

That doesn't mean that a 500 is a good UX. We give error messages on invalid form input for a reason.