Personally I will leave the experts to answer that. Being a lay person I see it as having two options with a variety of outcomes but only one positive.
*) Your Salaah is Valid if the Imam had done an act contrary to your school as long as it is from their school and they are not "pick and mix"ing things
1) You pray behind the Imam
2) You don't pray behind the Imam
Outcomes
1) You pray without a doubt and all is well
2) You know its wrong yet you pray - your playing with your Deen
3) You don't know its wrong - your still playing with your Deen.
4) You cant decide then its better to be safe than sorry.
5) If the Ulama have erred in their fatwa, they will have one reward and there's no sin on those who follow.
Ask yourself, would you like to be safe rather than sorry.
Conclusion
Go safe.
Allahu alum, and I'm sure we can add a lot more to the outcomes


