If MediaHandler::doTransform called to transform the file, then the second argument ($dstPath) is a file path to the output file. However, if its called with self::TRANSFORM_LATER because file already exists, then the $dstPath argument is a mwstore:// url. This is rather inconsistent (I suppose its because we don't want to copy over the file in that case to get a local ref.) Not sure what could be done about it, other then document more clearly.
[This is a rather low priority bug]
Version: 1.23.0
Severity: normal