I should have mentioned this in my original post but I'm very familiar with the vent settings in Idrive and all vents are set to blow warm air. And it's been cold here for weeks so if it was related to the vent settings I would have noticed it awhile ago. This was a situation where yesterday morning, while on "auto" all vents blew warm air - Got in the car to leave work later in the day and all vents blew cold except defrost which blew warm.
I've done a fair amount of searching and most of what I've found has to do with all vents blowing cold not this situation where the defrost vents still deliver warm air
2005 545i Black Sapphire Metallic - Sport/Premium/Cold Weather
2007 328xi coupe/Auto/sport/premium/black saph/saddle-turned in Aug. 2010
1983 Porsche 944/5sp/Gemini Gray