When the person you want to attack if is in infirmary or in isolation it shows up..

The same way i think the Attack",mug,raid buttons should also be inactive if they are in different prison.

the link of those buttons can be removed i mean.why the hell u click on those buttons without watching that they are in different prison,and get instructed that they are in different prison and u cannot attack them" like that.

It can be fast identified that they are in different prison if u remove the link and make it to red color or the same u use for offline users.