SPSS file record layout type 2 vs type 3

[Pascal Heus]

All:
Does anyone now the exact meaning of the record layout type byte present 
in the SPSS .sav file header? This is byte #65 that follows the $FL2 
signature and the 60-byte information string. According to the 
documentation I found and based on source codes, the only allowed values 
are 2=SPSS file and 3=portable file. Problem is that I have recently 
received a few files produced I think with SPSS 12 or 13 that have a 
layout code = 3 (not sure why) but look exactly like a record layout 2 
file. I'm trying to figure out where this difference comes from.
thanks
*P