Tested with the latest SVN version. Sending files or screenshots from Spark to Spark client. On the sending side it shows that the file was sent. On the receiving side it always shows progress bar with some amount of KB received. I think it always shows some percent of the whole file size. If it just a small png screenshot, it always shows 1.4 KB is sent. If i send 1 MB file, then it shows 80 KB is sent. Files are received and you can open them just fine. Spark is just not showing sending animation and never ends it.