Bob said _No the problem occurs for no reason no bounce
Bob your best bet for keeping the date stable is to use a piece of software like Atomic Clock Sync to set the clock from an atomic clock. If the server does not have access directly to the internet set up a proxy (I use Proxy Plus) to allow a connection only to the atomic clock you prefere to use. (Depends on where you are located.)
You can set this to once a day or once an hour (low bandwidth) and at least your clock will be correct most of the time.
Why it is changing could be a number of things. The prime reason ofr clocks changing is probably human error. You seem to have removed this as a possibility so we are left with software errors since you indicate that the problem is not happening at boot. (The cmos is only read by the OS at boot.)
So the problem is probably a piece of software that accesses the clock or is interupting the timer tick. If you have any significant software running that stops the timertick or interupts it for a long period of time this can cause clock slowing. If the software is running in this state for close to an hour you would see the problem you seem to have.
Other issues could be that you or software or users are logging into a second network and that networks time is used to set the clock. On windows networks this can happen. SO do you connect to a network that needs a login that is in a different time zone?
Other then that software that is setting the clock wrong?
Hope this helps.