.gz files inside a tar file aren't uncompressed

[Chris Moore]

I have a tar archive which contains (amongst other files) a gzipped file.

If I extract the tar file to disk, then Emacs will automatically
uncompress the gzipped file when I visit it, but if I open the tar
file in Emacs (it opens in Tar mode) and try to visit the gzipped file
it doesn't get uncompressed, and I see binary junk.

In the buffer (which gets named "file.txt.gz (file.tar)" by tar mode)
these are the minor modes that are enabled:

Enabled minor modes: Auto-Compression Blink-Cursor File-Name-Shadow
Font-Lock Global-Font-Lock Line-Number Menu-Bar Mouse-Wheel Tool-Bar
Tooltip Unify-8859-On-Encoding Utf-Translate-Cjk

Putting compressed files into a tar file (which will probably be
compressed later itself) might sound unusual, but some applications
(inkscape, for instance) often save their documents gzipped to save
space.