(Originally mis-sent with the wrong email address.)

Attached is a patch with tests to fix this. Note that I reset 
`eshell-in-pipeline-p' in two places:

1. `eshell-subcommand-bindings': This handles any case where a 
subcommand is invoked. This can happen with the following syntaxes: 
{CMD}, ${CMD}, and $<CMD>.

2. `eshell-command-to-value': This handles cases where a command is run 
synchronously. This can happen with some of the syntaxes mentioned 
above: {CMD} and ${CMD}. However, it can also happen for Lisp forms like 
(LISP) and $(LISP). (Most Lisp forms aren't likely to consult 
`eshell-in-pipeline-p', but if you were calling an Eshell built-in 
command using Lisp syntax, you might run into this issue.)