Client is spammed with unknown packet if mod is installed only server-side

[Owgla]

If a server has the mod installed and a player joins it the player log is spammed with "Unknown custom packed identifier: flycommand:no_fall_mark_packet" multiple times a second.
It makes reading log files extremely hard, I have no idea what causes it since it seems to be spammed regardless of whether the player is currently flying or using the mod itself in any way.

This is not a game-breaking bug or anything like that, but it is really inconvenient and makes it hard to do any debugging.

(I also can only paste in the first 2002 lines because of size constraints, the total log is in two parts on my drive totaling 31865 lines)
https://pastebin.com/jLZmYG6P

(Here are the full logs)
2022-12-15-4.log.gz
2022-12-16-1.log.gz

[hamusuke0323]

ok, thx for issue. but it is general. server sends the packet, but client-side has not handler to handle the packet(the packet is not registered), then logs like it. probably, other mods that are installed only server-side may make the logs spammed.