When the posts are longer the forum software doesn't even bother to try and understand the stupidity of the posts (which is a common thing on Interlopers). When its shorter, it'll often have a go at it, making it longer for the message to be posted.
We call her Rosetta, she's a good forum.
I be talking out of my ass! But I think your question might just be an illusion, I don't think I've ever experienced this problem.