Ever since some time last night, I get asked to type a verification every time sometimes when I log in.

I've noticed a couple blank lines after the login MOTD for many weeks now, but is that actually sending chat to the server somehow?

Attached is a screenshot demonstrating what's going on... it's not that much of a hassle, but I am curious as to why it's happening.

You have bacon, what's the problem?

Yeah, I don't think those spaces are supposed to be there... Do you have any mods that could be affecting the way your chat works?

I use OptiFine and the WorldEdit CUI mod, however it looks like two blank lines are still inserted even when I use a default .jar.

There seems to be a 1-2 second delay between receiving the MOTD and the two blank lines showing up, enough time for other people's chat to get in between.

Attached is what I see immediately after logging in when I DON'T receive a spamming notification. Could this be related to being in a clan?

I suggest backing up your client, returning back to being completely unmodded (including removing extra mod files/folders), and then reinstall WECUI and Optifine. Even though it's not echoing into chat, you're spamming the command /worldedit cui when you log in.

Two blank lines also appear when I log in. I have macro mod and reis minimap.

SPECTACULAR! I've trimmed out the old fluff from my minecraft folder and next time I login I'll see if I can get that to stop. Thank you for the sleuthing!