I was pondering this question this afternoon because I was scheduled to meet with a Level II candidate for tutoring this evening. I came up with this:
If the functional currency is different from the presentation currency, then the subsidiary is essentially acting autonomously; i.e., not under the control or influence of the parent. The parent doesn’t take responsibility for the subsidiary’s decisions, and the subsidiary only occasionally (i.e., yearly) passes information along to the parent so that the parent can present their financial statements. Thus, the information is translated using the current method: the parent only gets to see how the subsidiary looks at the moment the information is reported. Furthermore, the parent isn’t responsible for translation gains/losses as it is nothing more than a reporting conduit; thus, they start with the income statement (on which they do not show a gain/loss), then move to the balance sheet; the gain/loss is included in OCI but is not part of the parent’s income.
If the functional currency is different from the local currency, then the parent is taking full responsibility for the actions of the subsidiary; as soon as the subsidiary engages in any transaction, the parent owns it. Thus, the information is remeasured using the temporal method: the parent treats all transactions as if it had done them itself, at the time they occurred. Furthermore, the parent takes responsibility for any foreign currency gains/losses; thus, they start with the balance sheet, then move to the income statement; the gain/loss in included in the income statement as part of the parent’s income.
(It seems reasonable to me, anyway.)