Seagate back up plus 1 tb reloads when I plug in or plug out the power

[Ujb78600]

I have an external hard drive Seagate backup plus 1 tb working fine with Sony vaio E15136 win 8.1 64 bit 4gb Ram. As long as I change the power supply i.e either plug in or plug out the power supply of my laptop, external drive is re-detected.
The external drive draws power from laptop.No external power source.
In case of USB pen drives this thing didn't happen.
Looking for any solution or explanation?

 

[ComputerGeek]

1. Is the laptop plugged in when this happens? (could be a power issue)
2. Other then that, i'd check for any BIOS updates for the laptop
3. And any firmware upgrades for the drive

 

[Ujb78600]

Re-detection just happens when I plug in or plug out the laptop charger
BIOS software is upto date as per official vaio website
External hard drive is plug and play ,doesn't need any software although comes with Seagate dashboard software....