Yes, that's a known limitation. It would require a lot of added complexity in the parser to get the quoting with {{{... }}} do the right thing for nested {{{ or }}} pairs, and in practice it's not really needed, as there is the other quoting ` ... ` which can be used to embed triple curly braces when needed.
The above paragraph itself demonstrate this. See its corresponding Wiki text:
... to get the quoting with `{{{... }}}` do the right thing for
nested `{{{` or `}}}` pairs, and in practice it's not really needed,
as there is the other quoting {{{` ... `}}} which can be used to
embed triple curly braces when needed.
