SOLUTION: This was a bug in bash which is fixed in patch bash4.2-029. See
I build from source as follows:
- downlaod bash-4.2.tar.gz from ftp://ftp.gnu.org/pub/gnu/bash/
- download patches bash42-001 through bash42-029 (actually I did all through 037) from ftp://ftp.gnu.org/pub/gnu/bash/bash-4.2-patches/
- apply patches
- ./configure --prefix=/usr/local; make; make install
Using this /usr/local/bash fixes the problem -- tab completion on environment variables works again.
Can these patches please be applied to the package in precise and oneiric?