The code uses a histogram to determine what the default attributes for an extension should be. When the rijndael_*.txt files were added, there were more *.txt files with CRLF than with LF, thus the default to CRLF. When the autodoc documentation files were renamed to *.txt the balance switched.
Ok, that's an explanation but not a reason. ;-) I suggest overriding the decision in this case.
As far as I can see, the original test supported either, but Nilsson's commit "No \r in the testdata anymore." removed the support for \r\n.
Ah, right you are. But the bottom line is still that crlf conversion should not be enabled after the change.