Matchmaking declines / dodges

It seems to me that once you are assigned a position in matchmaking, if someone dodges, you should be "locked" into that position. Almost every time someone dodges a match, I end up getting autofilled to another position (usually bot or supp).

The result is that it's better for me to cancel matchmaking after someone dodges and restart, causing me to have to wait another 3 min or so.

TL;DR (rly?): Once you get into champ selection, you should be locked to your role/position, even if someone dodges.