TinyMCE strips src attributes from <script> tags

If you paste some HTML source into TinyMCE containing a script tag with src attribute, like:

<script src="http://widgets.twimg.com/j/2/widget.js"></script>

TinyMCE will strip the src attribute and leave <script></script> there.

This happens for all users, including those with trusted content capability.

I believe this is a bug because:
a) Moodle 1.9 used to allow this, and it's necessary for embedding things such as twitter widgets, etc into HTML blocks.
b) If I turn off javascript and circumvent TinyMCE, I can paste my script tags into the textfield and save it without problems. So it's not Moodle that strips it, it's TinyMCE.