Why did the Soviets occupy Bornholm for so long?

A quick investigation of the issue shows that the Soviets stayed in Bornholm for almost a year after occupying it. What I don't get is - why? The obvious idea is that the Soviets wanted to keep the island for strategic reasons, but there are two issues I can think of: first, they left without much of a fuss in 1946, April, with only a condition that NATO troops aside from those of Denmark wouldn't be stationed there, and second, I have found no evidence that Denmark or any of its allies were engaged in tense negotiations with the Soviets throughout this 11-month period. One would think that the proto-NATO would have pressed for the resolution of the Bornholm issue sooner. At the same time, I can't find any sort of agreement between Denmark and the USSR regarding the occupation, either. So, what's up with this?
 
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