It depends on the license of the piece. Some of the pieces on there are commercial copyrighted works. All three of mine (that I've found) are CC licensed, so it's less of an issue. However if one of the maps I've done for publication turned up there, then I could get in trouble with the company - which is not really what I'm after.

Their direct contact seems to be down so I've posted directly to their forums with a complaint. I'll let you know how I get on.