This problem can be seen in images from any of my lenses. It mostly occurs when using flash, but I have seen it occasionally in other shots. This example is enlarged from a very small portion of the original image.
It looks to me to be some sort of reflections on the sensor, as the 'bubbles' are sharp whether the area is in a focussed or defocussed area of the image.
Despite searching the web, I have yet to come up with an answer.
Someone on here must have either come across this problem, or know the answer.
Any help/ideas welcome.