Oooh, that also annoys me that city planners do something like that.  Yeah technically that should also be marked as a "roundabout" though it's too small to actually take advantage of the key aspect of the structure: you have right of way when you're in in the structure and all people entering it must yield.  I think the other thing is that if you needed to take a left turn in the new intersection, do you turn right?

If these two aspects are not met then it probably shouldn't be tagged as a roundabout especially if the latter isn't met and perhaps traffic calming island is a better choice.  Are there photographs of the intersection anywhere?