My SLA timer is not resumed after I pause it or viceversa

Hi,

I have set my SLA to pause , when status is in OnHold and again restart , when the status is In Progress..

But sometime it is not restarting (Occers only when my Case type is request)the timer when I change the status to Inprogress or Vice versa.. That is when the timer is running I cannot pause the timer by using OnHold .

First of all I paused my timer by setting SLA status to "On hold" then when I change the status to In Progress again , it must work..But the timer still remains in Paused state.. Pls reffer diagram 

but in my settings I have configured right ..

pls help..