Originally Posted by rockcavera
I tested the previous versions, the error starts in version 7.53. That is, version 7.52 was the last one that the command worked on.


rockavera: Indeed. That's the version where all the messaging commands had a major overhaul and unification internally.

Code
29/11/2018 - mIRC v7.53
20.Added /privmsg command.
21.Added support for CPRIVMSG and CNOTICE. If listed in numeric 005,
   PRIVMSG and NOTICE will be automatically upgraded for most
   outgoing messages if you are an op/voice on a channel and message
   a user on the same channel.
22.Added support for numeric 005 STATUSMSG=@+ and WALLVOICES and added
  commands /vmsg, /vnotice, and /wallvoices. If server does not support
  STATUSMSG, WALLCHOPS, or WALLVOICES, mIRC uses own method to send to
  multiple targets.
23.Changed line splitting method for long messages when:
   1) Sending message through editbox of a channel/query window.
   2) Using commands /ame /amsg /describe /me /msg /omsg /privmsg /qme
   /qmsg /query /sound /vmsg /wallchops.

   Note: when line splitting, the /sound command switches to an ACTION
   message for the second line onwards.

   Note: line splitting is not performed on NOTICEs, so is not applied
   to /notice /onotice /vnotice /wallvoices.

24.Changed multiple target handling in PRIVMSG and NOTICE so that if
   TARGMAX or MAXTARGETS are not specified in numeric 005, mIRC assumes
   the maximum is one target per message.

Well. At least I won lunch.
Good philosophy, see good in bad, I like!