Sure it is. The toggleToc() code is doing just document.cookie = "hidetoc=1".
"If [path is] not specified, defaults to the current path of the current document location". so your assessment is right.

I think we should do instead:
document.cookie = 'hidetoc=7; path=' + escape( wgArticlePath.replace("$1", "") );

(note that I use escape because it leaves / untranslated but escapes ;, not sure if there may be any other dangerours characters)

During the rewrite of mediawiki.legacy (of which wikibits.js' toggleToc is a part of) this will be taken care off.

Adding to resourceloader tracking.

Fixed in r78941.

Cookie is now set domain wide instead of just the local path.

The bug that caused the TOC-setting to only apply to the current article or subpage - and being inconsistent depending on the view (ie. action=purge from scriptpath was different then viewing the same article from articlepath ("/w/"index.php?title=This vs. "/wiki/"This ) – is now fixed.

Should be live on translatewiki.net tomorrow.