mIRC hangs upon saving a (non-ini) popup file that ends with blank lines. The hang occurs before writing the file. The hang does not occur with aliases, remotes, users, or variables.
Thanks this issue has been fixed for the next version. The issue was not specific to Wine, it also happened when running under Windows when a rich editbox was not available (which is rare). mIRC uses different code for processing text in non-rich editboxes which made the issue appear under Wine.