Thank you for making the correction.

Superb, good work and many thanks for the feedback. But I think there's going to be some confusion.
Since English is not my mother tongue I use a translator and he either doesn't translate correctly or I don't understand these two sentences.

"This is the Signal audio clip"
It may be right but I don't understand this sentence. But for me it doesn't fit the function. I think its 15 seconds "represent the background noise that the filter uses as a reference". So I would translate it more like that.

"This is the whole Noise Audio clip"
For me, once again, I understand this sentence. For my part, I would replace it by "represents the recording whose filter should remove the background noise".

"This has the effect of creating a keyframe that marks the beginning of the reference range, reported in point 1which, in our example, ends at 65536 samples later. "
For greater clarity, I also propose to amend the above text as follows:

This has the effect of creating a key frame that marks the beginning of the reference range, mentioned in point 1, which in our example ends at 65536 samples later.

https://cinelerra-gg.org/download/CinelerraGG_Manual/DenoiseFFT.html

Personally, I confirm that I arrive at the same result after tests on several other effects.
So, unless I'm mistaken, I think it's normal.

No problem. English isn't my first language either. And thanks for taking the time to explain.

Let's assume you have two clips of 10 seconds. The first one is on track 1 from time 0s to 10s. You attach an effect (say gain) to it. The effect applies to a time range as well. By default it is the same as the track from 0s to 10s.

When you add clip2 on track 2. Maybe that clip isn't starting at the beginning, maybe it goes from 5s to 15s. When you attach the shared effect to track 2, cinelerra puts the shared effect from 0s to 15s.

However when you render the project, it appears the effect only applies from 0s to 10s and it drops at 10s. So the effect did apply on the whole clip on track1, but only half the clip on track2.

However, if you adjust the time the effect applies on track 1 to the time range 0s to 15s, then the effect applies to both clip "as intended".

Is that correct?

Sorry, the instructions I put are wrong and apply to "Shared tracks". I have edited point 3- and I attach a clarifying video here:
https://drive.google.com/file/d/1HF0ntqzJeZLjFrP7s-C5gN1iifYcaoVo/view?usp=sharing

PS: Due to my poor English, I also didn't quite understand your last message.

@Godrik
I would like to answer your question but I don't quite understand your explanation.
Please give me some details so that I can really understand your problem.

OK that worked. Thanks!

@andreapaz

OK, I think I understand. Thank you for the explanation!

I assume RMB is "Right Mouse Button"

If I have an effect on track 1 that I want to copy on track 2, it seems that the span of applicability of the effect on track 1 need to include when the effect needed on track 2. And even if track1 is done by the time track 2 starts. Is that right?

Thank you, I have added your description.
If you read through the manual and see that there is something to correct or improve, feel free to propose your own revision. Audio plugins are the most overlooked due to lack of expertise, but any section of the manual is just as good. The manual is a work in progress: the more contributions we receive, the better the result will be.