Hi Andrey,
No, it is not normal to have a leak of air in the back hole of the device. This can only means that the internal gel/diaphragm is damaged.
This kind of issue is typically caused due to an excessive pressure applied to the sensor, a negative pressure (vacuum) was applied to the sensor, temperatures below/above the specified in the datasheet or because it has being used to measure pressure in a different media than “Dry clean air”. If none of this is true for your case, then it is probable that the pressure sensor is defective.
Have a great day,
Jose
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