I'm running into this now, too, though in Posts.xml. I'm still importing, but I stripped some
from post id 854536. I edited the source post so it doesn't continue to get put into the Posts.xml file, but it will continue to exist in PostHistory.xml as a revision. (Edit: here is the other post. Those two were the only ones blocking the Posts.xml import for me.)
This is a real problem, because these invalid characters don't allow the files to validate as XML 1.0. It seems most parsers (including the one I'm using) don't support XML 1.1, so I'm not sure simply changing the header to 1.1 would be very helpful.
Since the invalid characters (so far) are of the non-printing, garbage type, I think we may be able to get an assist from the dev team to strip these out directly in the database, so we don't have to go through a ridiculous search-and-replace process every time there's a new data dump. (It wouldn't be so bad if the big XML files were pre-split into smaller chunks, but still.)
Okay, I got both Posts.xml and PostHistory.xml imported. All that's needed is to remove the entities
. Easier said than done, I know; those are big files. I ended up doing a file split on both of them to track down the errors, but since I've done that already, the next time, I would recommend just opening each big file as-is in an editor and doing search/replace.
That said, this should still be fixed in the dump itself.