1. Bug#1. All archives created by $zip have the 'y' attribute, which is supposed to mean they're some kind of temp file:
//remove testzip.zip | echo -a $zip(testzip.zip,c,$mircini) | echo -a $file(testzip.zip).attr
2. There are a few filenames that return $null as an attribute even though 'n' is the attribute for 'no attribute'.
Part of this is the known issue here https://forums.mirc.com/ubbthreads.php/topics/45625/re-mirc-6-1-global-bug-still-there#Post45625
due to the filename (excluding the .extension) matching one of the windows device names. It prevents /write from or $read to filenames whose prefix matches one of the device names. i.e. "/write global.txt test" fails, and even when the file exists $read(global.txt,nt) returns $null.
While that part's a known issue, there are a few other filenames which also return .attr null, such as pagefile.sys and hiberfil.sys, but they aren't device names, and you can write to pagefile.sys without trouble. Depending on how deep you want to search, this shows all filenames where .attr returns $null:
//echo 3 -a $findfile(c:\,*,0,3,if ($file($parms).attr == $null) echo 4 -ag $file($parms).attr $parms)