B1 visa - i94 they stamped with B2 and 6 months validity

my friend came on B1 visa a week back at NY. at port of entry the officer stamped i94 with B2 and validity till july 2013 i.e 6 months.

Is that a mistake? because B2 is a different purpose altogether.

and B2 has more validity whereas B1 should have less. and should have been granted less validity.

if its an issue then what is the solution?

Thanks

The officer can grant maximum 6 months on B-1 or B-2. They can be interchageably used for tourism and business purposes.