The only reason Whatsapp doesn't have this issue is that it doesn't allow you to login with the same account on multiple devices like Skype does.
Both use the same underlying technology (XMPP) and both know how to use the protocol, but it's still very hard to pull off at this scale once you allow multiple devices to login with the same account.
Skype just has vastly more features, that's why they have these synchronisation issues.
Both use the same underlying technology (XMPP) and both know how to use the protocol, but it's still very hard to pull off at this scale once you allow multiple devices to login with the same account.
Skype just has vastly more features, that's why they have these synchronisation issues.