Still doesn't make sense why the Soviets were willing to break a promise and expect the other side to respect theirs. Unilaterally accepting Japan's surrender is a huge deal - no one will trust the Soviets after that.
Either side will want to immediately press an advantage here, citing the Soviets' previous move as justification. I can see this Cold War turning hot very soon post-war, especially since there isn't the threat of nukes to restrain them.
Actually, the fact the US is close to developing the first A-bomb should embolden them in acting more aggressively in Europe to contain Soviet influence.
I think unconditional surrender for Japan had been butterflied away, as that conference couldn't have happened in ATL. In the eyes of the Soviets, they were merely mediating the peace that they felt was deserved considering their position of strength relative to the late-comer WAllies. The west sees this as more of a separate peace and thus a broaching of the the alliance.
Japan hasn't promised anything, they negotiated to retain what they could and are in no position to resist.
Stalin only promised he'd help in the war in Japan.
The west promised to help bring down Germany, which they didn't really do, except mop up the rear. The west didn't get around to liberating any of the territory the Japanese held except some fringes like Burma and New Guinea.
As far as Stalin sees, the WAllies are weak and slow and don't deserve as big a slice of the pie.
There will be huge tensions on asia over the colonies that were not returned, and Europe is even more tense.
While the Americans will soon be having the bomb, the Soviets completely outmatch them on conventional front in Europe; they wouldn't risk it.
Each side will focus on digesting their new gains before the next big conflict.