Unfortunately, there is no patch. Retainage is setup in AR, as you know. QIP calculates based on the retainage % that is setup in AR 1st, if there is an amount entered. If there is no retainage percentage entered in the AR Housekeeping field, you can enter your own flat amount, but posting will send the retainage amount calculated based on the result of what you have entered into the Totals screen in QIP. As you have seen, as soon as you enter the $40210 into the retainage total field in QIP, it calculates (and rounds up) the percentage.

This is likely based on the fact that you have a 2-decimal place currency code setup for AR, thus for QIP. You must choose a percentage based on 2-decimal places if you wish to have a consistent value posted to AR and GL.