I was very surprised to find that this doesn't work. It's old behavior and it doesn't agree with how CMD behaves.
Code:
v:\> type b1.bat
@echo off
b2.bat | findstr foo
v:\> type b2.bat
@echo off
echo foo
echo bar
v:\> b1.bat
foo
bar
v:\> cmd /c b1.bat
foo
v:\>