Do frame sampling and frame blending add frames when they don't need to?

I posted a question about frame-rates when slowing down a video a week ago and only got one response and no answers.   So I've been trying to research it on my own.   The entire question is here:

https://community.adobe.com/t5/Premiere-Pro/Playback-speed-question/m-p/10685560#M233080

...but a brief synopsis is that when I used Speed/Duration to slow a 5 second 120 fps clip down by 4X, it did indeed slow it down by 4X but it seemed to add frames in the process because the output was 20 seconds at 60 fps!  

I had tried both Frame Sampling and Frame blending and got the same result.   The documentation for those says . . .

Frame Sampling repeats or removes frames as required, to reach the desired speed. Frame Blending repeats frames, and it also blends between them as required, to help smooth out the motion.

... I assumed it would repeat frames to keep the output from going too slow and flickering.  E.g.,, if I had a 24fps clip and slowed it down by 2X it would make 12 fps, which would flicker, so to avoid that it would insert or blend-in extra frames.   But my experiment suggests it adds extra frames even when it doesn't need to, like in my case where if it hadn't added frames it would yield 30 fps, which would be fine and not flicker.    But it added the extra frames anyway.  Why?   Is there a way I can force it to not do that?

Thanks In Advance!

PS - Forum Question:  at the bottom it says, "Topics help users find your post. Please select one or more topics."  But NONE of the suggested topics comes close!  Is there a place I can add my own keyords or see a bigger list?   TIA