I am assuming your talking about a forum photo block which is a hack or mod normally. If your talking about the photopost application you most definately would have to provide accurate information like url and example so we can assist otherwise all we can do is guess based on what it appears your trying to explain which alot of times may not be what the issue is.
There is nothing in the actual photopost application that does not have a slash between the data url and category number. I see nothing broken here
http://joinphotography.com/photopost/