> BUT the filter appears to be ignored after the 
> first '&'.  This causes many more files than i need 
to 
> be downloaded.

Ensure that you defined strict filters, if you defined:
+www.foo.com/bar/foo*.html

This will cause the engine to accept all foo*.html 
files in /bar, but ALSO other files, for example that 
might be present in the same directory. By default, 
HTTrack will catch all files on the same domain and 
same directory / subdirectories.

To avoid that, define something like:

-* +www.foo.com/bar/foo*.html