Help - how does the Semi-Automatic diaphragm on early Auto Takumars work?

I should know this (and maybe I do!) but I currently only have one Auto Takumar (the 35mm f2.3) and want to make sure the functions are as they should be.

These "semi-automatic diaphragm" lenses have a cocking mechanism on the lens which consists of a protruding finger/thumb knob that you press down to set the lens to fully open (the aperture setting can be at any number before you do this) - this means when looking through the viewfinder you see a maximum aperture brightness image and then when you press the shutter button the lens stops down to the aperture you had selected .

What I'm not sure of is when you press down the knob should it then stay in the position you set it to or should it slowly rotate back to original position (while keeping the aperture wide open)?

None of this matters to me when I'm taking photos on a digital camera as I would shoot stopped down anyway - but I would like to know if my lens operates as it should for when it gets passed on to an m42 film shooter.

I hope I've explained it well enough to be understood? Hopefully one of you knowledgeable people can advise

I’ll check my Auto-Tak 55/2.2 in a moment which has the semi-auto diaphragm. If I recall rightly it does spring when that ‘knob’ is clicked to open the aperture fully but I’ll make sure that I’ve recalled it correctly.
Thereafter there’s a little protrusion in the base of the lens which, when pressed, releases the aperture to the set value.