No, its not normal, but also not unusual for solenoid pneumatic valves. You can CAREFULLY disassemble the valve (there are springs and other small parts inside, and orientation of several parts is critical), removing the "shuttle", which has several O-rings on it. Slather some silicone grease (available at any auto parts store) on the o-rings, and re-assemble. If that does not fix it, you can try replacing the o-rings, though they may be an oddball metric size.

Regards,
Ray L.