Unable to find anything in the changelog regarding this so I'm assuming it's a bug. /queue/simple/print no longer gives access to the statistica properties; IE what you get when running '/queue simple print stats' at the console.
RouterOS Version 4.11
15/08/2010 09.34.25 - info 102 - EXECUTE= /queue/simple/print =.proplist=name,bytes,packets
15/08/2010 09.34.25 - DEBUG 11001 - 10.0.0.1 tr_mkrouter.msend /queue/simple/print
15/08/2010 09.34.25 - DEBUG 11001 - 10.0.0.1 tr_mkrouter.msend =.proplist=name,bytes,packets
!re=name=foo
!re=name=bar
!re=name=baz
RouterOS Version 4.4
15/08/2010 09.34.25 - info 102 - EXECUTE= /queue/simple/print =.proplist=name,bytes,packets
15/08/2010 09.34.25 - DEBUG 11001 - 10.0.0.2 tr_mkrouter.msend /queue/simple/print
15/08/2010 09.34.25 - DEBUG 11001 - 10.0.0.2 tr_mkrouter.msend =.proplist=name,bytes,packets
!re=name=foo=bytes=0/0=packets=0/0
!re=name=bar=bytes=0/392=packets=0/8
!re=name=baz=bytes=979/0=packets=14/0
This is happening on both the Delphi API client as well as my Perl API client. Communication works properly, the router simply doesn't respond to the bytes or packets properties. Don't have a full suite of RouterOS revisions to test against so I'm unable to give a hard verion where this behavior started. However, I'm fairly certain I have this code running against routerOS as new as 4.6 with no issues.
Edit: Checked, most recent revision I have running that exhibits the latter behavior is 4.5.