There are a lot of invalid feeds of RSS/Atom in the world.
But we cannot fix the feed by ourselves. (just claim it)
Then, you can use 'tidy' for such a purpose.
With d3pipes 0.61, we added a joint D3pipesReplaceTidy4xml.
Just insert 'tidy4xml' before xml parser.
You will receive such invalid RSS/Atom into your XOOPS.