mediaelementplayer.min.css and wp-mediaelement.css loading twice in WordPress 3.9-RC2 on TinyMCE pages

[n7studios]

Using the latest WordPress (3.9-RC2), I have noticed that mediaelementplayer.min.css and wp-mediaelement.css are loading twice, once in WordPress, and once through TinyMCE - on any page that loads TinyMCE.

On an admin page that does not load TinyMCE, these files are not loaded at all (expected behaviour). I have attached a screenshot of Chrome's Network > Stylesheets tab which indicates the files being loaded more than once each.

Do these files need to be loaded twice (a total of four times across both files), or should they just be loaded once each?

This was discovered as we were investigating an issue in relation to the limits of CSS styles that can be loaded in IE6-9. More information on this issue in IE is available here: ​http://support.microsoft.com/kb/262161

[n7studios]

Chrome Network > Stylesheets

[ocean90]

That's correct. The reasons therefore is, that TinyMCE uses an iframe for the content. In this iframe we have to load the files again. Same for dashicons.css btw.