certain URL must be disguised

AFAIU, WXC uses filters (plz don't ask me what and why). So, if you wanted to post with a link like that, you need to disguise it. That is to fool it around. For example, you may insert one or more # (pound) signs into the URL, like this:
ht#tp://cn.pi#aoyao.org/modules/mydownloads/viewcat.ph#p?cid=4 ( I chose the places for # randomly).

Don't forget to remind of the readers that they need to remove the # signs when copying and pasting the URL.

Good luck.