Initially, check 9.256/log/bootlog for the boot history. This will show you instances where the PacketShaper has booted, and the symbol on the right indicates the reason the reboot took place. This is elaborated in 000010191
If the PacketShaper shows several "-" symbols in a row when attempting to boot the desired version, followed by a successful boot to the previous version, the shaper was either crashing, or unable to load this image successfully, and self-reverted.
If the PacketShaper shows a successful boot into the new version with a "+" at the end, followed by a successful boot into the previous version also with a "+" at the end, the appliance is being instructed to upgrade/downgrade by a user or by PolicyCenter.
PolicyCenter can be configured to have a "prescribed image." If the PacketShaper is running any version other than the prescribed image, PolicyCenter will move the PacketShaper back to the version prescribed.(See PacketGuide for details.)
You may change the prescribed image to the desired version, or set it to "none" to allow the device to be locally configured.