I don't see this in Firefox 13/Linux either in the deployment on mediawiki.org or locally. Any details on when/where this happens?

Occurs in Chrome/Mac and Safari/Mac, but not Firefox/Mac.

Resultant HTML:

<div class="es-tool es-toolbarDropdownTool es-toolbarDropdownTool-format" title="&lt;visualeditor-formatdropdown-tooltip&gt;">

&lt;visualeditor-formatdropdown-tooltip&gt;

(individual entries don't have tooltips assigned)

Presumably this is meant to use [[MediaWiki:Visualeditor-formatdropdown-tooltip]] which is unititialised on MW.org - but setting it to something doesn't fix the problem:

http://www.mediawiki.org/wiki/MediaWiki:Visualeditor-formatdropdown-tooltip

From perusing the code I think it's in the messages array but missing from the i18n file, and not called by modules/ve/ui/tools/ve.ui.FormatDropdownTool.js, but it's got beyond my patience when rooting around with nano. :-)

Thank you James.
Fixed in https://gerrit.wikimedia.org/r/14599