Is it possible to have kepubs on different devices without them getting locked?

Hi,

I currently have 4 kobo's (2 wireless, 1 mini and 1 glo). I use the same account for all 4 devices.

My question is this, when I update my devices libraries I tend to do all 4 at once. However I am noticing that the kepubs are being locked on my 2 wireless devices. Is their any way around this other than sideloading them onto the 2 wireless kobo's?

Thanks
Nascarfan1972