This looks like a bug.
We are importing bulk devices from a recipe by uploading a CSV with custom values for tags. The key/value pairs for the tags look correct on the preview. Then after import, the value for the first column of the csv representing one of the tags repeats for about half the records, and another value for the other half. The tag values are all unique in the preview as they should be. But the imported result causes the values of those two tags to be repeated over and over. It appears that the first tag value in the first row repeats and then the second tag value about halfway down then repeats for the remainder.
Its very odd and hard to describe!