Been having a similar problem just in automatic mode (without using Manual mode). More than a few times, when trying to accelerate the engine just revs (like it's been shifted into neutral or it dropped into a lower gear like others have said). Since I'm in the automatic mode I don't seen any change to what gear I'm in, and "so far" no flashing lights. The car seems to be fine afterwards, but my confidence in the CX-5 is starting to erode.
Mileage has been pretty good - on normal weeks driving to work (55 mph, but with some traffic lights) I get around 32 mpg. With more city driving I get around 29-30. Oh and I have 11,000 miles on it now.