Previously, if a device temporarily failed the kernel would notice the interruption and regard the device failed. The kernel needs to be notified before it regards the device as alive again. LVM, however, would be able to see the device and 'lvs' would report the device as operating normally (i.e. without the partial attribute) - even though the kernel still regarded the device as failed. The user had to use 'dmsetup' in order to find out the true state of the device.
Now 'lvs' will print a 'p' (partial) attribute if a device is missing and will also print a 'r' (refresh/replace) if the device is present but the kernel regards the device as still missing. Upon seeing an 'r' attribute for a RAID logical volume, the user can then decide if the array should be refresh (reloaded into the kernel using 'lvchange --refresh') or if the device should be replaced.