Hi Tony,
Can you please repost the url you have mentioned above. I am also facing a similar problem while working with edittype:'custom'. When opened in the edit mode, myvalue function (custom_value:myvalue) gets called only once (which is alright) but in the edit modal popup if you change the rows, the myvalue function does not get called. The same data remains populated in the custom control with different rows.
Regards,
Simrat