Your recommended steps do not capture what's going on with this bug. It's necessary to be using ZNC for this to make any sense. The echoed message is received by all clients connected to ZNC, not just the client that sent the message.

Originally Posted by Client A
-> yosemite.snoonet.org PRIVMSG mem2 :first message
<- @time=2022-05-18T16:38:34.899Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG mem2 :first message


Originally Posted by Client B
<- @time=2022-05-18T16:38:34.899Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG mem2 :first message


Client A and Client B are both connected through ZNC with nick Membear.

Client A sends message to other nick "mem2". Both Client A and Client B receive the echo for this sent message. In Client B this opens a query window for its own nick Membear, it's supposed to be in a window for "mem2". A remote text event is triggered for this message, which I dislike because it's an echo of an outgoing message not a real incoming message. In this case at least you can check if the message was an echo because it lists the address of the sending nick and the string of the nick it was sent to.

Messaging yourself makes this even worse

Originally Posted by Client A
-> yosemite.snoonet.org PRIVMSG membear :first message
<- @time=2022-05-18T16:54:06.977Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG membear :first message
<- @time=2022-05-18T16:54:07.014Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG Membear :first message


Client A receives both the incoming and echoed message, and processes one of them as a remote event.

Originally Posted by Client B
<- @time=2022-05-18T16:54:06.977Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG membear :first message
<- @time=2022-05-18T16:54:07.014Z :Membear!membear@Snoonet-lu490c.tvts.k9oe.ul59e5.IP PRIVMSG Membear :first message


Client B receives both the incoming and echoed message and processed both of them as remote events.

In this case the address of the sending nick and the nick it was sent to are the same, so it doesn't appear to be possible to detect if one of these messages was an echo. This feature just doesn't seem compatible with ZNC.

https://imgur.com/a/J3UTBEV