Documents are locked when opened under XC UI Testing

Got an issue with XC UI Testing where I can't open documents without them being marked as locked (the Locked label is shown in the titlebar).

The document in question is a testing asset and copied into the testing bundle for easy access. I've checked the file in bundle in Finder and the document is not marked as locked.

I've also tried copying the document to a temp directory before opening it and it's still locked?!

What's the trick for getting it to open without being locked?