It's like having only 7 teams left to form the last Level leagues.. what they do is pick another 7 guys that finished 8th and place them in a higher level to complete the numbers to 14.

ex: Lv 30 had 15 different leagues and a total of 210 teams, 105 of them were meant to be promoted..
As you could simply calculate thats 105:14 = 7.5.. now that's 7 full leagues of 14 teams and 1 league with only 7 teams in, they randomlly
select another 7 teams that finish 8th(from their previouse 15 leagues) to fill up the 8th league.

This happened to me few times but i was actually happy about it cause it was on an alt team, wasn't trying to tank a season..the competition was just hard enough ..
Anyhow if your trying to tank, always look for 10th or below that... can't go wrong.