Ah, found it…
It is a matter of terminology. Specifically, the terms now used are “collect” instead of the old “raid”
Here is the excerpt from LHTR…
Capturing and Liberating Capitals
If you capture a territory containing an enemy capital (Washington, Moscow, London, Berlin, or Tokyo), follow the same procedure as for capturing a territory. Add the captured territoryâ€s income value to your national production. In addition, you collect all unspent IPCs from the former owner of the captured capital.
Notice that it says that you COLLECT income (emphasis added above), you do not raid it, seize it, or anything else, you COLLECT it.
Then there is this…
PHASE 7: COLLECT INCOME
In this phase, you earn production income to finance future attacks and strategies. Look up your powerâ€s national production level (indicated by your control marker) on the National Production Chart, and collect that number of IPCs from the bank. Double-check your income by counting up the value of all the territories you control.
If your capital is under an enemy powerâ€s control, you cannot collect income. A power cannot lend or give IPCs to another power, even if both powers are on the same side.
So… since you COLLECT the IPC’s held by the enemy if you take their capital, and if you CANNOT COLLECT income when your own capital is enemy held… you do NOT get the money for taking an enemy capital when your own has fallen.