Chapter 12 of the FAA Airplane Flying Handbook, discussing multiengine flying, goes into quite a bit of detail in the propeller section about how most feathering-propeller-equipped engines on multiengine aircraft have a mechanism that prevents the propeller from feathering if the engine RPM is below a certain value, before mentioning that one particular widely-used turboprop model does not have this mechanism:
As just described, a loss of oil pressure from the propeller governor allows the counterweights, spring, and/or dome charge to drive the blades to feather. Logically then, the propeller blades should feather every time an engine is shut down as oil pressure falls to zero. Yet, this does not occur. Preventing this is a small pin in the pitch changing mechanism of the propeller hub that does not allow the propeller blades to feather once rpm drops below approximately 800. The pin senses a lack of centrifugal force from propeller rotation and falls into place, preventing the blades from feathering. Therefore, if a propeller is to be feathered, it must be done before engine rpm decays below approximately 800. On one popular model of turboprop engine, the propeller blades do, in fact, feather with each shutdown. This propeller is not equipped with such centrifugally-operated pins due to a unique engine design. [FAA Airplane Flying Handbook (FAA-H-8083-3B), Chapter 12 ("Transition to Multiengine Airplanes"), my emphasis.]
What is the identity of this standout, and what unique aspect of its design is the reason for this difference from other feathering-propeller-driving engines?