fixes #1482

This addresses a bug identified in #1482, whereby mustaches on one side of an unresolved component mapping wouldn't update immediately when the mapping was resolved.

@martypdx @evs-chris I haven't quite got my head round the mapping changes yet, so I'd be grateful for a sanity check...
Thanks. Have to admit I don't understand it well enough to construct a test case yet! Reckon it might be better to merge this in as-is, then at least we've ticked off the bug we know about. If there's one we *don't* know about, I'm sure it'll introduce itself soon enough