Interesting bug (or feature) with copying keys

I encountered an interesting bug (or feature) when copying keys. Please, see file attached.
test_copy.blend (953 KB)
Take bone “center_top” (selected in the file). I have keys on X Scale and Z Scale curves and on Y Location curve. They look almost the same, but they are different and were created by inserting keys by hand, not by copying from each other. I wand to copy, say, X Scale keys to Y Scale curve (in order not to make them by hand). Instead, Blender copies keys not from X Scale curve to Y Scale curve, but from Y Location curve to Y Scale curve, although I did not select or copy from Y Location!
And what is more interesting, if I delete Y Location curve keys, and try to copy from X Scale to Y Scale, there will be no keys pasted at all!
And furthermore, if there are keys at Y Rotation and at Y Location and I try to copy X Scale to Y Scale, it will choose Y Location to copy from…

There is some hidden logic in it, but it seems more like a bug, sorry :eek:

Could you help me to just copy keys from X Scale to Y Scale?
For I’ve got lots of flying objects in that tower and I’ve got lots of copying to make. And I cannot do it for some queer reason…

Thanks in advance.

And this is not the first time I encounter this question… Though copying different keys on different bones on different curves is one of the common technics with animating process!

Since there has been no answer, and since it looks like a bug, I reported it at