A conflict would arise if the central bank would have to address the two objectives with only one instrument, i.e. the interest rate. The central bank could be pushed to use the interest rate not only to achieve price stability but also to counter macro systemic risks.
For instance, it could have to increase interest rates prematurely, in order to stop a financial bubble from developing, while the underlying economic developments do not require it. The interest rate is not necessarily the most efficient way to prevent or to prick bubbles.