Collapse menu button not working if browser size is 911px width

[alexvorn2]

After I added a metabox to the edit page of the post, from here:

​http://codex.wordpress.org/Function_Reference/add_meta_box

the collapse but does not work if the browser size is 911px, need to refresh the page after resize to see the bug.

My browser is Firefox (latest), Windows 7

I use this for browser size check - ​http://whatsmy.browsersize.com/

Confirmed in Firefox by resizing the browser window to 911px using Web Developer extension. Nothing happens after clicking the "Collapse menu" link.

Adding a meta box is not relevant, confirmed without that as well.

Related: #21795

ticket:21795:21795.diff​ appears to fix this.

Confirmed. Happens for body width between 884px and 899px (as reported by Firebug's "Layout"). Caused by difference in calculating the body width, i.e. the responsive css kicks in at 883px rather than at 899px. Seems the 15px difference is caused by the width of the scrollbar, works properly if there's no vertical scrollbar.

@Sergey, this is currently a double-double switch:

• Above 900px is sets 'folded' or 'auto'.
• Below 900px is sets "unfolded' or 'auto'.

The 'auto' is handled with responsive css. We could make it a normal three-way switch: always folded, always unfolded or auto, perhaps by changing the text "Collapse menu" to "Auto collapse" and the icon to... something else than arrow.

Moving to 3.6 as #21795 has a fix which is set for 3.6 already.