i have a 36 hp boiler and use industrial steam engines directly connected to it. Smaragd- and gold energy pipes to transfer energy to an ender io starage bank (40m rf can be stored at 40.000 rf/t input/output)
thing is all industrial engines work and transfer power (80rf/t) and they all build internat power up, more than 260.000, which gets not transfered and is rising over time, engine is red at the moment..
is that build up and raise of storing of rf a bug?

No. The engines stabilize around the orange stage currently.