pkgsrc on Windows 7 64 with Interix 6.1 (10.0.6030.0) bmake error "pkg_create: user 197608 unknown"

[Matteo Fabbri <m.fabbri%softlab.it@localhost>]

I have correctly installed the bootstrap kit on my Interix 6.1  
(10.0.6030.0) environment under Windows 7 64, but when I try to  
install packages with bmake I receive an error like this:

...
pkg_create: user 197608 unknown
*** Error code 2
...

197608 is the uid of my Windows user under Interix and pkgsrc seems  
not able to recognize this as a valid user for pkg_create command.
I have also setted umask to 002 as suggested by installation notes on  
Interix subsystems.
Any ideas for solve this problem?
matt