Heres my thoughts,
Changing the pref from bright 100 to on makes sense, as i'm sure you've noticed there is a "charge up" time when you are dimming a module. Using the Bright 100 setting you are telling it to use the dimmer function but at full brightness, if it just has to turn the power on to the module, that is of course going to be a lot faster. There is a delay on almost all of the trancievers from x10 i've noticed. When using a remote to turn a light on it takes maybe 2 seconds before that light actually turns on. Almost as if there is processing time. Your pc can obviously process faster then the CM15A, so perhaps that is why it is faster when going through the pc. I dont know how you have the macro setup but if the dog continuously triggers the sensor it will trigger the macro several times, perhaps before it is even completed the first time... That might also be causing some of the delay, i'm not sure. Might want to call X10 and look into buying the SmartMacro software if its a concern.