Painting - Bubbles when I paint over venetian plaster

The home I recently purchased has venetian plaster walls in one room. Although I love the look, the color is way too dark for me. The former owner told me I could paint over them. I just started priming over my walls in order to paint them a lighter color. When I got one wall mostly primed, I noticed bubbles popping up on the wall. They range from as small as the tip of an ink pen up to dime size. They are squishy when you touch them, as if the wall is rubber and someone pumped air under the plaster. Sanding over the primer and painting again just produced more bubbles. What can I do?

If its a true Venetian plaster, it is rubbed with some type of wax to produce the glow it has. It should be primed with an alkyd bonding primer.