gnucash depends on gtkhtml, which depends on control-center. I unmerged control-center, and emerged gnucash, expecting emerge to say, "hey, I need control-center because gtkhtml needs it". gtkhtml was installed. Anyway, it went ahead and tried to build gnucash, and did, and installed it, and control-center is still not installed.
yes, but did gnucash work?
Not sure it would have. I emerged control-center again, before running it, just to be safe.
portage currently does not resolve several steps backwards, so this is "not a bug", if an ebuild requires a feature directly to build it has to put a direct dependency on it.