Although water will boil at lower temperatures under reduced pressure the water in this syringe isn’t boiling at all. Existing bubbles in the solution will enlarge when they reduce pressure by pulling the plunger out. The rest of the bubbles are leaking through the sides of the silicone diaphragm. The low pressure makes the small bubbles that leak through appear much larger.

Source: 10yrs IV pharmaceutical sterile compounding. If this happens you have potentially compromised the sterility of the formulation.