Weird to have show start airing before filming is even done.... 
Didn't they do that last year too?
Yes, the show had already started airing right before the last block of filming, but If I am remembering it right, they even managed to add some footage from the finale leg into some or the early season episodes. Which is justified for S4, due to the theme of the season. as the Summer Olympic Games were about to start
HCM City next.
Then a break...Last two episodes (Macau and Shanghai Finale) will be filmed mid August.
Air date may have been pushed back a week. 
Weird to have show start airing before filming is even done.... 
Curious if they'll be scrapping Kuala Lumpur, which is listed among the cities from the first promo. Is the only one missing from the checklist. Kuala Lumpur was listed between Macau and Shanghai in the promo.
They're probably at HCM already. Teams spotted at airports flying there already, but unlike most TAR versions, unless there was a task ahead, flying time usually not considered racing time.