Sometimes when using the left-right arrows to go to a keyframe, the keyframe does not get selected and you have to click on it yourself. This is annoying but that's the way it is. So, click on the keyframe to turn it on - blue - and then delete.
BTW, you can select multiple keyframes and move or delete them.
I cannot reproduce the issue, either using your method as shown in your video clip, or by my method shown below using VPX 22.0.1.244, which patch version of VPX 16 are you using?
It is strange indeed, over the years I have come to the conclusion that subtle hardware and more likely Windows differences can make or break whether i can reproduce issues, I think this may be the case here.
I tested on my laptop, cannot confirm on PC for a few more days, however from experience, with Windows installations of 100+ identical PC's, subtle differences with a small percentage of them could, and did, occur.
I wrote the text with the test version (22.0.1.215 / UDC2). Note that last year, I only didn't buy it because after testing with VPX15 another annoying bug wasn't fixed (clips moved to the project folder are limited to one second). I contacted support, who confirmed the bug. So I figured that one year would be enough for them to fix it. So I downloaded this version to test and confirmed it again with a new ticket to the technical area. "This time even the owner noticed! " So I thought I should go deeper into the tests. Now I see that there is version ... 244! So I'm taking advantage of this question: do you have any history of the items that you fixed since this version 215?
My version of MMS214 doesn't have the same defect that I showed!
I can almost consistently show/repeat the non-selection of keyframes but it usually happens on the second time keyframing is used, that is a second object and beyond.
Try this. Put 2 images on the timeline. Apply Camera/Zoom Shot to the first - Custom, change the rectangle, move along the timeline, change the rectangle, a few times so get some keyframes. Use the arrows to go back and forth to the kfs.
Go to the second image and do the same. Use the arrows to go to next/previous kf does not select the keyframe - doesn't turn on blue.
Go back to the first image, arrows to select kfs works. Go the second, arrows don"t select the kf. The playback marker moves there.
Worse, but intermittent. On the second object, select a kf, change the rectangle. Occasionally a second kf gets put at that location. I see this as there is a jump and using the arrows to go to the kf, then when pressing to the next one the playback marker stays at that location as there is a second kf there. I just tried to reproduce this but can't. Grrr.
I have almost finished a tutorial on CZS and had a lot of trouble with this.
Image 1 - the KF's are added however the SPR effect in the keyframe pane is not automatically selected when the 1st and subsequent KF's are added. I have to click the SPR header to activate, and can then step through the KF's.
Image 2 - behaves the same as image 1.
Did I miss anything?
The duplication of a KF I have seen before and is as you say intermittent.
Roberto already wrote this: "I contacted support, who confirmed the bug and I had already been able to reproduce this problem".
John EB gave me this answer on September 28 at 13:28: "It is strange indeed, over the years I have come to the conclusion that subtle hardware and more likely Windows differences can make or break whether I can reproduce issues, I think this may be the case here".
After reading your answer and watching your video, you confirm my findings. Thanks👍 for that.
I will submit everything to Magix Support Germany.
Best wishes, Rob
PS. in Pro X13 on my other computer I was able to reproduce this BUG