One suggestion.... Make it faster to skip back and set the start date, or allow manual entry. I'm not even that old but it's a lot of months to click backwards on Android.
Ah, sorry about that. It is the native date picker as n8cpdx pointed out.
I just pushed an update to only update the grid of weeks once the date picker is unfocused (onblur event) rather than recomputing unnecessarily on every change event. I suspect that is what caused the bug you're describing, but let me know if it's still broken.