Increasingly this year, China and Russia have been undertaking more military cooperation. This indicates that long standing disputes over Chinese theft of Russian military technology have, at long last, been settled. Late last year, Russia and China signed an agreement (Agreement on the Protection of Intellectual Property Rights of Russian Weapons), in which China promised to stop stealing Russian military technology. It appears that the main function of the new "military technical cooperation" agreement was to stop China from exporting their copies of Russian equipment, and competing with the Russian originals. At the time the agreement was signed, it was unclear how enthusiastically the Chinese would adhere to the deal.
For the last six years, the Russian government has been trying to deal with the growing problem Russian defense manufacturers have had with China tolerating, or even encouraging, Chinese manufacturers to steal Russian military technology. It's not usually entire weapons systems the Chinese are stealing (like aircraft or ships), but components. Radars and electronic systems in particular were being copied, often using samples and technical data provided by Russian manufacturers, in anticipation of a sale. What often happened was that there was no sale, and then, a few years later, the Chinese came out with a copy, often a blatant copy, of the Russian radar, missile or electronic warfare gear.
All this is ironic for the Russians. During the Cold War, much Western military and civilian technology was blatantly copied, including microprocessors and computers themselves, by the Russians. Since the end of the Cold War, Russia has been more careful about this, because the collapse of the Soviet Union opened up the Russian defense labs, and their large store of discoveries that had not been developed into anything useful yet. American manufacturers were eager to get rights to this technology, once they got a good look at it. The Western firms paid, and the billions of dollars that entered the Russian economy that way forced the Russians to reciprocate, and pay for Western technology they wanted.
The Chinese have been forced by the West to cut back on some of their blatant theft of foreign technology, except for Russian military stuff. The Russians are getting fed up, and the government is under growing pressure to crack down on the Chinese theft. But there's not a lot the Russians can do, and the Chinese know it.