It appears the internal permissions are '10440' (the leading 1 being wafl-specific) and then the resultant string is sliced to the first 4 chars (rather than masking it off). For example, chmod'ing a legit sticky bit onto the file (1440) yields:
The behavior follows if a file is copied (either via ZAPI or NFS), but a new file created via NFS shows the correct behavior.
This is in the root volume, with a unix qtree style, so it wouldn't seem to be shenanigans from a mixed security style. Seeing this on both 8.0.1P5 and 7.3.2P4 systems, haven't bothered hunting for other variants.