The sport's governing, the Badminton World Federation, has long been concerned about players withdrawing from 'smaller' events and team mates pulling out of matches to avoid competing against each other.
The issue blew up at last year's London Olympics when four women's doubles pairs from China, South Korea and Indonesia deliberately played to lose their matches in order to get a more favourable draw.
The BWF disqualified all four pairings and banned them after the farcical scenes sullied the sport's reputation and sent shockwaves through the Olympic tournament.
In Jakarta, Du lost 21-15 15-21 21-9 to home favourite Rumbaka to leave China, the dominant force in world badminton and the winner of all five gold medals in London, without a player in the men's singles or doubles.
While Du credited the impressive play of Rumbaka for the surprise defeat, more sceptical observers said Chinese shuttlers save themselves for bigger events and do not take the smaller tournaments, like the $700,000 Indonesian event, seriously.
"I don't want to take any credit away from Hayom but Pengyu hardly gave a fight in the rubber game," Malaysia coach Rashid Sidek was quoted as saying by the Malaysian Star.
"Pengyu is the top seed in the Singapore Open next week but I won't be surprised if he does not live up to the billing.
"These players are more concerned with the world meet and will not push themselves as they do not want to risk any injuries. So, if you ask me, their defeats should not be taken seriously."
Du said people were reading too much into his defeat on Friday.
"It is normal in every tournament, there are wins and losses. I did not play very well today while Hayom was outstanding out there with his strong smashes and defence," the world number three told Indonesian media.
Rumbaka said he had been expecting a tougher test.
"I never expected to win this easily. Compared to my two previous matches against him, it was pretty easy. I am glad with my performance today," he said.
Rumbaka will take on top seed and world number one Lee Chong Wei of Malaysia in the last four on Saturday for a place in the final against the winner of the other semi between Germany's Marc Zwiebler and Tommy Sugiarto of Indonesia.