The "bleeds on" situation is this: Taking bleed air away from the compressor means less air is available to turn the turbine, so the fuel/air ratio gets a little richer as the FCU (or FADEC) tries to maintain engine RPM or EPR.
This results in higher EGT, not healthy for longevity of the hot parts.
So the engine power management calls for a decrement in EPR (or N1) to try to keep EGT back to original level. Thus thrust is a bit reduced for bleeds on.