ok, looking at your conf, you have 5 other teams in. there *might* be a logical explanation here, but i cant see the projection report at the time, nor the ultimate seeding, which is what i would need to say for sure. but without a doubt, it seems to me for this to be "expected behavior", FOUR of your conferences mates MUST have taken spots in the four bottom-half regions. there are additional constraints but i think that is the bare minimum, and given those four, i could believe it might be possible for the other constraints to be met (no region having a spot for you due to a conf mate being there, until the one you got into, is really what needs to be met).
so, if you look in each region, is one of your conference mates a 2, 3, 6, 7, 10, 11, 14, or 15 seed? really, those 14/15 seeds would not satisfy the constraint, if those teams were lower than you on the projection report.
if the answer is YES, all 4 regions have a conf mate, this may not be a bug. however, id send a ticket regardless. dropping from a 13 to a 16 is ridiculous, and i think that is probably a pretty ubiquitous opinion. but still, a "hey this isnt working" ticket and a "hey this is stupid" ticket are a little different, and if you send the former, and it turns out to be working, it seems like seble and co tend to ignore follow up arguments of the second variety. not ignore, but, care less maybe?