I don't know why the release notes say it is fixed. I have made the same experience as you.
However, the workaround is, you have to double the backslashes compared to version 2.49a, eight backslashes to have two backslahes in the output:
say "\\\\"
Another workaound is using the unicode hex value. This was new introduced in 2.49b. The unicode hex value for a backslash is "005c". Write "\u005c" to get one backslash. For two backslashes
say "\u005c\u005c"
Here is a German topic about the same issue:
[F] Mp3tag 2.49b: Änderungen bei Web Sources?
Have a look at the test script I attached to the last post there, this will make things clear.