This can occur but is preventable. To avoid condensation in the sealed air gap we recommend applying the membrane system when the air humidity is low. You should also check that there is no moisture trapped between the glass and the frame, that windows fit properly into the frames, that timber is well seasoned, and that any paintwork or silicon sealant is thoroughly cured.
If you discover condensation between the membrane and the glass, it can be removed by carefully lifting a small area of one corner of membrane to allow air movement. Wait for a day when the humidity is low, and then re-seal the membrane to the corner.