"Some Chinese websites suggest that Moscow sold Beijing SU-27 fighters on the condition that they remain south of the Yangtze River, a sizable distance from the Russian border."
Okay now something happening. The Russian won't want the Chinese near their borders with fighter, Unless the conspiracy goes deeper.
Those who fear Chinese dominance over far-east Russia in a longer turn (15-20 years) are quite correct in my opinion. And weapons once sold Chinese may turn right against the salesmen.