I suspect the problem is that you're creating datacell objects from scratch, rather than retrieving them. Try using GetDataCell instead, and it should give you cells that are as expected.
This said, this all smells of an anti-pattern. You shouldn't need to start from cells to build buffers; instead, you retrieve buffers and only go to cell level if strictly necessary, getting them from the buffers. If you build a buffer from scratch, you typically populate it with cells that are copies of cells you retrieved in some other buffer. Let OneStream sweat on the details of object creation.
