Concrete 5.6.3.5 and broken RSS-feed

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I have an old installation (version 5.6.3.5) and rss-feed has stopped working after this update. Problem seems to be with XML-validation. The first line is not:
<?xml version="1.0" ?>

but instead there is there is two empty extra lines:
01.
02.
03. <?xml version="1.0" encoding="UTF-8" ?>

And this causes that XML does not validate and browsers give an error.

I checked file "/concrete/blocks/page_list/tools/blog_rss.php" and there is no any extra lines, so these two lines comes probably from the core of the C5. In which file this could be happening?