Could this be what he's after?
A reader points out that what we're referring to as the "Istook Amendment" doesn't sound like an 'amendment', properly speaking. If I understand what happened correctly, this was language slipped during reconciliation. The phrase comes from the AP article quoting Sen. Bill Frist. And I don't know whether Frist misspoke or the AP misquoted him.
In any case, this language raises an interesting point and may give us some indication of what Rep. Istook was after.
If you do a Google search for "Istook Amendment" you'll get quite a number of hits. There've been at least two Istook Amendments before this one. But the phrase is most commonly associated with an amendment Istook tried to get attached to a number of bills in the mid-90s that would have placed tough restrictions on political advocacy by tax exempt organizations that receive federal funds.
Here's an example that illustrates the issue -- and I preface this with a warning that I'm sure I'll be oversimplifying or getting some nuances of the issue wrong.
Planned Parenthood may receive a federal grant for, say, doing an STD awareness program or doing free STD testing in low income areas. Planned Parenthood also does public advocacy on behalf of birth control and sex ed. and abortion rights. The federal grant is dedicated specifically at that one program while the advocacy work is funded by foundation grants or private contributions or whatever.
Istook would say, all money's fungible. So same difference. The federal government is actually funding Planned Parenthood's lobbying on behalf of reproductive rights.
Let's set aside for the moment whether his argument makes sense. If you were really interested in this issue -- as Istook clearly is -- you'd be very interested in seeing the tax returns of the organizations in question to see if they're really segregating the money as they say they are.
So maybe that's what this was all about. That's just speculation, of course. But there was clearly some motive behind this. The language in the provision is too specific and carefully crafted to admit of any 'accident' explanation.