I recall this warning for an engine failure during a high power climb, not for during a turn. Can you repeat the passage that concerns you, or state the section from which it comes?
The warning I recall related to the UH-1H during sudden lowering of the lever during high power climb outs if suffering an engine failure. This had to do with the massive resultant pitch down change (airflow over rear stabiliser PLUS sudden lack of collective pitch ), the subsequent rapid unloading of the disc into negative g territory followed by the roll coupling causing a bank angle with an unloaded disc. And then mast bump if not corrected properly. Where are you Lu Zuckermann???