[quote=Tick]
Hey Mahz, what's causing the nesting issue?
[/quote]

I don't often work with regexp. 

One issue is that if you want to parse "[tag][/tag] [tag][/tag]", then it seems reasonable to match the closest [/tag] for every [tag].

But what if it's nested? "[tag][tag][/tag][/tag]". Well, now the first [tag] is going to match the first [/tag] and break the nested tag.

When I have time, I will write a proper parser for BBCode without regexp. This is something I've done before: [url=http://bbcode.herokuapp.com/]demo[/url].

Nested quotes and hiders aren't even really on my priority list. But I do need to improve the quote button, roll out a preview feature, and add editor buttons so that people don't need to type it manually.