I don't know how the internals of the keyboard work, but by doing testing I'm now pretty sure that the problem I have with the XPS inserting multiple spaces frequently is a mechanical one.

Testcase: Press space and any letter of your choice in  quick succession. For example just type 

d d d d d d d d d d......

Don't use your usual typing position, but just use your index fingers for both keys. Now while you're  typing those alternating keys, notice that when you  move to the edge of the spacebar (left and right end, and also vary the point towards the screen and towards the touchpad), the double-space problem occurs, while it never occurs when pressing it in  the center, no matter how fast you  type (and the alternating between regular letter and space is only to see the double-spaces). 

As I have my thumbs below the "m" and "c" and thus hit  the spacebar at the  corners, I'm prone to triggering the  problem frequently.

Please comment whether you confirm those observations (no double-space when using center of spacebar, double-spaces when  using the edge of the  spacebar) or not.

(German Keyboard layout on XPS 13, FullHD, i5)