What shell were you using that didn't give you a count of the lines in both data1 and data2?

I tested the last snippet under Linux-x86 (Slackware 10), and NetBSD-sparc 1.6.2, and using bash and ksh93. In both cases I got a count of the lines in both files data1 and data2.

Those of you seeing a count of the file "data1 data2" instead need to document what shells and systems you are seeing this on.