Report Builder Filter Breaks When Removing/Adding Fields

I am having the problem of when I am building reports and i remove or add fields and click run it changes whatever complicated filter i had ie A AND  B AND (C OR D OR E OR F) AND G to all ANDS and it breaks the report showing no data. It happens often, I have to copy the filter and paste it back in and even when I do that it gives a weird invalid expression message at saving at first then I click save and it allows me to run it then.