Linked to the manual on the CZ-USA website.
https://czusamedia.s3.amazonaws.com/files/Instruction-Manual-cz-75-SP-01-Shadow_en.pdfPlease look at Page 9.
This talks about the correct working of the Single Action Manual Safety.
Engaging the Safety
Push the safety up to the Safety-On position (Fig.5) until the red warning dot is covered.
The safety in this position blocks the trigger mechanism and slide, thus preventing the pulling of the trigger and operating the slide.
Since the trigger mechanism has been specifically adjusted, it is possible to move the safety onto the "SAFE" position even if the hammer is placed on the safety notch or leaned against the slide.
In this case, however, it is not recommended to engage the safety because the trigger mechanism might be damaged when cocking the hammer by force.
Besides the method previously described it is possible to put the pistol into a safety mode and still be ready to fire immediately:
Load the pistol.
Grasp the grip, POINT IN A SAFE DIRECTION. With a thumb press on the grooved area (thumb piece) of the hammer, pull the trigger and release the hammer slowly forward (Fig. 6) until it rests on the action or safety notch of the hammer.
Release the trigger.
Practice this operation very carefully to avoid an accidental discharge! We strongly recommend to practice this operation beforehand wit h the pistol unloaded!
In this state the pistol is safe for all normal handling and at the same time ready for immediate use.
Please remember that the safest way to secure a pistol is to unload it and store it in a safe place!
This indicates that it is indeed possible to engage the Single Action saftey in the Hammer Fully Down and Half Cock positions, but that the pistol is not designed to work that way and that either puling the trigger or thumb cocking the pistol with the safety engaged can cause damage to the internal components.
