What makes you think it's cloudflare blocking this?  Wouldn't it make more sense that it's code within the forum infrastructure that is altering the code as it may be possible to exploit it somehow?  That would be my first guess and seems to be the most logical.  Are you seeing something that makes you think cloudflare is altering your posts?  Personally, I don't think that's what cloudflare does, or is capable of doing.  I thought of that service as a router of data and to block malicious attacks, not alter text for users who are trying to use the protected website.  Seems like one of us is missing something here.