I'd posted this bug earlier also , but apparently no one cared to answer , however i found this bug again so I'm posting this the second time
Guys check this out and confirm it , whenever i re crew some heavy weapon with the sappers they somehow seem to retain their repair ability , you just select an AT gun re crewed by sappers and then point at a damaged vehicle , they will repair it
This i think is surely a bug , guys please check this out on your games too , i'm not sure but i think this happens only with sappers upgraded with overrepair
