When I looked at the 2 boxes they had the same model number on them, but one was a dark grey and the other was white. I think the white ones listed SB as compatible. At the time I doubted that they were different models since a miniDP is a miniDP, but now that I saw your post I wonder if the older models didn't have the clearance for the SB.
When I go to the MS store site, there are multiple ways to navigate around and I can find 2 different HDMI adapters. One is listed as "Mini DisplayPort to HDMI Adapter" and lists SB compatibility and has a very small non-angled miniDP end. The other is listed as "Surface Mini DisplayPort HDMI AV Adapter" and talks about SP3/S3 and has a miniDP connector that is thinner and longer than the HDMI end.
Then there is this page which lists the latter of those 2 accessories and the miniDP end of it clearly looks tilted, though the relative sizes of the HDMI and miniDP ends are not the same as you see when you click on it:
Microsoft Surface Tablets
On the BB web site there are 2 SKUs for the adapters and the one that doesn't mention SB is on a clearance currently:
Microsoft - Surface Mini DisplayPort-to-HDMI Adapter - Gray
As opposed to this one that is not on clearance:
Microsoft - Mini DisplayPort-to-HDMI Adapter for Microsoft Surface 3, Surface Pro 3 and 4 and Surface Book - Black
Unfortunately, they don't show pictures of the boxes on the web site...
But, clearly MS had a different adapter before the SB came out and I wouldn't be surprised if it didn't ditch the angle in the connector when they updated it...