$address($nick,5) seems to be broken on 7.52.

Here's the output:

Guest8282!ggedTweets@icqchat-chm.1mo.595cca.IP

instead of

Guest8282!RaggedTweets@icqchat-chm.1mo.595cca.IP

tested on inspircd 2.0 .. seems to work for short idents,.. starts not showing the correct ident starting at 10 chars

No it's not, it's related to using too-long userid's longer than 10, look at the topic right before yours:

https://forums.mirc.com/ubbthreads.php/topics/262892/bug_in_identifiers_$address_an

Even though userid's of length 10 are "sorta" supported, it's a good idea to use 9 or shorter, because when the identd handshake fails, they insert a ~ at the front, and that pushes one of your 10 out of the address.

We don't use the ident server (~) in our idents, as its not 100% needed. Means its a mirc bug

The bug is the person who went into their irc client and input a userid longer than 10. The link I gave you has a link to another thread where that's all discussed. They're not going to "fix" this behavior if it's going to blow up existing scripts that expect the old behavior.

This is by design. Please follow the links mentioned by maroon as there have been several discussions about this before.