If you are not using the AC, I could see this happening while the IMA batteries are TOO hot. I live in DFW area of Texas, and have not noticed this. I USE my AC, btw! (AUTO, set to 76-80.)
I'll be on the lookout for it, though. I can't imagine I've missed this though, if it happens as frequently as you are experiencing it.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL