Post Preview no longer shows UNAUTHORISED_BBCODE warning for disallowed BBcodes

In phpBB 3.0, if you tried to use a BBcode that is not allowed (i.e.: flash), you get an error message (UNAUTHORISED_BBCODE) when you try to submit and/or preview.

In phpBB 3.1, you only get that error message when you submit.

When you preview, there is no longer that error message, and instead the bbcode is displayed in its broken/un-rendered state in the preview.