simfactory's sync command uses rsync with the --archive (-a) option. This option set the modification date of files on the target machine to that on the source machine. This can lead to inconsistent builds in the following situation:
 local: edit source_file.c  local: simfactory sync  local: edit source_file.c  remote: simfactory build  local: simfactory sync  remote: simfactory build
 will not rebuild source_file.o since  set the modification time to that of  which which is older than  hence make will not consider source_file.o to be out-of-date.
A simple fix is to add --no-times to the rsync options. Unfortunately this disables rsync's file modification time optimization and requires it to compute checksums on all files which can be very slow on slow filesystems.