why “swPartLoadFromStorageNotify” can not be listened when I load a part file with 3rdPartyStorage?

Hi everyone:

    I want to save and load custom data calculated by my Add-in. And I use the "IGet3rdPartyStorage" api to do my work. I have met a problem, I can save the custom data when I save the xx.SLDPRT file by listening the "swPartSaveToStorageNotify" event.  But when I load the xx.SLDPRT file,  I can not receive the “swPartLoadFromStorageNotify” event .And I can recieve the "swPartLoadFromStorageNotify" event only when I create a new part file. I don't know why I can't receive the part-load event. Does anyone know about it?

Thank you

SolidworksApi macros