As described at http://www.kdenlive.org/mantis/view.php?id=3017 when kdenlive executes a render when one of the input files has a name ending with a space then melt creates a file with "invalid clip" as the output. JBM thinks this is due to melt
producer_xml.c line 546:
char *resource = trim( mlt_properties_get( properties, "resource" ) );
So I am guessing that melt trims of the spaces from the file name and then can not find the file resouces later on. Mlt should not bomb out on file names ending in space.