It's happened before, just depends on how technical you want to be and what you classify as a mid major. 2007 for example, had 3 (one from Morris Almond-Rice, Jason Smith-Colorado State, and Rodney Stuckey-Eastern Washington).
2009 had 4 (Tyreke Evans-Memphis, Stephon Curry-Davidson, Austin Daye-Gonzaga, Eric Maynor-VCU)