1996 Legacy with Manual Transmission: Won't start for a while after stalling it with the clutch

[Ravenwoods]

My daughter reported today that her 1996 Legacy (180,000 miles) this infrequent problem. If she accidentally stalls the car by letting out the clutch too fast the car doesn't want to start for a while. She says it's happened about five times in the last year or two. Typically she comes back after 30 minutes and then it starts. It cranks just fine but doesn't start. This morning it happened again and she only had time to wait 15 minutes but no success. So she borrowed my car. About seven hours later I went out and it started fine.

Any ideas what causes this?