There appears to be a bug with using slew mode that causes the 777 to dart forward after turning slew mode off. The pushback feature is not yet available in the 777's FMC or EFB but does work if you have GSX. Furthermore, there is a big with the built in pushbsck function (shift+P) where the tug connects but nothing happens.

So, don't use slew for pushback or this may happen to you. :)

Cheers & Blue Skes friends!!