You are off by about 0.36mA rather than 30 to 40 mA.
What multimeter are you using?
What is almost definitely occurring is the meter is loading the circuit. This is a well known phenomenon and can be corrected after the measurement if you know the details of the ammeter part of your multimeter.
Update
I looked at the user manual, and there are two current measurement ports on the meter you are using. As you are measuring below 4mA, try that range (if you are not already doing so.
The two setups are designed to minimise error based on measurement range.
HTH