Ping.fm misses/ignores/drops/fails to post some of my pictures

Sometimes (seemingly randomly) when I send a picture through ping.fm, it doesn't get posted. The picture is ignored and just the text goes through. I haven't figured out under what circumstances this happens, because sometimes I'll send exactly the same picture again and it gets posted the second time. What's going on at ping.fm that would make it just ignore/drop a picture from a post?