Various versions of PWSCF from summer 2011 produce an apparently miscompiled executable, which when told to print out a list of k points in the output file (or in xwfn.data), just prints out a string of zeroes i.e. all k points are listed as (0.0 0.0 0.0).
Having dug around in the PWSCF source code, it seems that the k point grid was being defined before the reciprocal lattice vectors, hence all the k points really were zero. I have no idea why no-one noticed this – you would think it would be pretty fundamental. Looking at the latest (26/11/2011) this has now been fixed.
Solution : upgrade your PWSCF.
EDIT: later investigation showed this problem was extant between commit 8051 and commit 8121.
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