Well, that was a particularly boneheaded suggestion on my part! That's not what tab completion does at all.
This appears to be a hardwired behavior into the IDE editor, since if you assign a triple spaced object in the console, you don't get the same behavior.
I suspect that this is a remnant of the great Two Spaces After a Period War that has consumed so much bandwidth since the advent of widespread proportional printing.
The output of knitting is, by default, proportional, and it ignores repeated whitespace. You'll see this if you knit
I am a sentence with many spaces.
I'm not exactly sure if this is the source of the rationale for this behavior--to fool the user into thinking that there really will be two spaces.
I should have asked before, though: What's the ultimate goal of being able to insert multiple explicit spaces?