Non responsive touchscreen when alarm activates

On 2 different Vivomove Style watches I have experienced that touchscreen will not always respond when alarm activates.  When it decides to not respond there is nothing I can do except to open App, disable the alarm and re-sync.  Both run latest 4.50 software.  In all other situations the screen is responsive.  It is ONLY alarm function, and NOT every time.  I suspect it is bug.