Problems with Maxim TQFN 38 pin part

I placed a Maxim MAX16810 38 pin TQFN with a power pad ground on the bottom of the chip on a prototype board FR4 doble sided.
Vias of 0.6 mm where placed underneath part, 6 vias in total. Solder was placed with an air operated syringe, land pattern was created according to manufacturer and vias where also recommended by manufacturer.

I placed part on pcb, hand assembled but reflowed, the part
apparently flew of pc board and landed upside down very near its
land pattern, I think that hot air from vias probably pushed
part upwards.

I have assembled many similar parts but this had never happened,
I also don�t know if this could of happened because vias are 0.6mm diameter. Maxim recommended 0.4mm vias.

Although part is not easy to hand place, its a prototype and in production it will be machine placed, but the problem was during reflow.

I tried a second time with vias filled with solder and part didn�t fly off but was shifted sideways and skewed, far from being acceptable.
Maxim doesn�t specify how much solder should be placed on power pad, on some parts its 50%, I placed close to 100% because of vias being filled and supposedly should draw out the hot air, but hot air goes up, not down...

Any previous experiencie with this part ??

Thanks,

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