Fix broken substitution $(b,...), $(i,...), etc.

It was broken in commit f5294f1b56dce20a1ffef998441c8407c744811f

This broke the output of all --help commands (no matter the output style).

I also added a test case to help prevent this from happening again.  You may want to add more.

It appears to work fine in v2.1, but v2.2 on Hackage is broken.