MM Pro BEC not holding voltage under load

[SpEEdyBL]

Upon running my Mamba Max Pro in my 8ight, i noticed that the LED's from both the esc and the transponder would flicker when turning the servo with noticeable performance issues. In fact, adding a slight resistance to the servo caused the transponder LED to turn off completely. My Mamba Monster does not have this problem, and neither does another's mm pro running the same servo (JR 9100s). This can't be solved with a "glich buster" capacitor, because this is a sustained current issue.

Is it just my unit that is bad or is this a common issue? If so, is this/has this been addressed by Castle? I would really like to continue being able to use my MM Pro in my 8th scale. It runs cool and is small and light.

May or may not matter:
Set bec at 6.0 volts
Used Zippy Flightmax 4000 mAh 40C 4s pack w/ Tekin 1900