It is unlikely that a probation department is going to be using the sort of home test kit that would be confounded by ibuprofen.
If you have a false positive, one option is to head right over to a hospital or clinic and get your own, independent toxicology screen to demonstrate that you had not used the substance at issue. Even that's not a perfect solution. You should talk to your lawyer about how receptive the court might be to an independent drug test, perhaps a hair test.

