Vanishing Rain in Saved Game

I've now seen an issue happen twice in rain races that I've saved midway through. The issue is that when the game is resumed, the track is dry. Sometimes the rain is still falling, and the track gets wet again within a few laps, but in the meantime we're driving around on wet tires on a dry track. The AI has even pitted (and my crew has called me into the pits) to change onto slicks. Does anyone know why this may be happening?