If you activate a resource booster right before settling you pay a reduced cost for activating but the bonuses still apply to the new city. This isn't a huge problem, but maybe it could be fixed by either adding an additional cost of 5 of each currently activated resource when settling or simply not letting the resource boost apply to cities founded after the activation.

This is not an exploit but intended design. It makes you think about when to optimnally use your boosters-/when to optimally settle.

By the way, same mechanic with influence for Empire plan(s).

ah yes, pack up all roving clan cities before the mark.