Is square bracket mark up working correctly ?
Well I am not sure but what I recolloect is wiki mark up [[square bracket]] used to still link to the article if I make a mistake of writing [[[square bracket]] like this. and after saving article it would show only exces bracket [ and rest of the link will work for square bracket article.
But the behaviour I spotted, while doing test edits is if I make the mistake of an writing additional [ then [[[square bracket]] after saving the article it will not provide [ + link to article but it will reproduce complete [[[square bracket]] text without parsing in the article.
Now this system will benefit if we had only one type of editing system of source editing.The user behaviour , which I spotted, with new visual editor and he comes across [[[square bracket]] this kind of text he is being shown a notice that there is wikimark up problem the new first time user will not understand notice also.
And the regular user but first time editing on visual editor, if happen to ignores the notice and still goes ahead to remove extra square bracket and goes on to save the text he and subsequent users editing the page will hit bug number 51462
So what I wish this issue is rather taken care of on mediawiki side and/or with the help of edit filer than that of fighting later at visual editor level.
Any way it is quite likely that developers are already woring on the ssue and this may be a duplicate bug too.But I wanted to report a user behaviour I spotted thanks and regards