auto-sync progress bar

Progress bar

Why is the auto-sync progress bar not accurate? and is there a workaround?
progress bar just doesn't work, workaround is - 

show auto-sync :<service-name> stats -i 1

or 

show auto-sync :<service-name> property trace_level 31

then watch

show auto-sync :<service-name> logtail -f

logtail will show you how much data will be transferred and how much is transferring per second.