Must be some sort of auto-something. Probably has something to do with the way the page is encoded. I remember from my typing class back in the dark ages that after a period, two spaces are required. But they don't show up here.
How come the number of spaces between "test", and the number, and "spaces" doesn't change
EX
I type "test"(then I hit the space bar twice) then type "2" (then I hit the space bar twice) then I type "spaces"
Then I repeat and increase the number of times I press the space bar by 1 each time.
When I preview the post, the spaces are all the same.
Hit Preview
It looks like this
test 2 spaces
test 3 spaces
test 4 spaces
test 5 spaces
test 6 spaces

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic