If you do /msg #chan1,#chan2 <message>, It will post <message> into #chan1 and #chan2, but it will only show you
-> *#chan1,#chan2* <message>
But not actually display the message as you post it per channel, which is a little annoying.

I don't even know any networks that allow multi-channel-target PRIVMSG commands, so I can't actually test this. What network are you trying this on?

And how are you even certain that the message went through, if you didn't see it in the channel?

irc.torn.com

Sent it to two channels my bot is on, and it viewed the messages correctly.

Confirmed, the message should display in the channel(s) but does not.

this has been this way through many versions, and i just assumed this was the way it was supposed to be. I had a script doing

/describe #chan1,#chan2 message

but always displayed

-> *#chan1,#chan2* message

in active window, so i had changed it to separate describes to get the message to display in channel.