update settings and transfer to properties

I have been trying to modify settings in the web presentation which are used to set a channel value which is used by a transform device to actuate a device when a trigger level is met and then turn off the device when the trigger level plus a Hysteresis value is met. all that works fine - EXCEPT:
I wrote a custom device based on the template device to change the trigger and hysteresis values. since the transform device wants a property and not a setting, I set up my “custom device” to have a setting for the two values has a property set function as a set_cb function. The run loop gets the setting and calls the prop_set function. The issue is several attempts need to be made to make the setting take in the device. (read click update settings 3-4 times while going up and checking the update box.
on an unsuccessful set, the info trace shows the setting changing to the requested value then immediately changing back to the previous value. This feels like a timing problem and what I think I really need to do is hook into the event that triggers the set_cb. but the persistant settings example has no associated XML file and when I try to mimic what it is doing either the settings do not show up in the presentation or the whole thing crashes. attached is my custom device python file.