Actually I did some more digging and I have to say, I’m not even sure how this could have been messed up.
I assumed the problem would come from the method prompting a window to select the asset. Those methods often do a lot more back-end stuff that could mess up things such as the clipboard. Those are usually located in the Plugin instance. And indeed, there it was:
Awesome, that is definitely what triggers the clipboard to empty, right? Right!?
Nope.
I decided to try making my own, see if there’s any issues happening, or any complication that could happen.
-- Note: I use the shared global table to access tools quickly in my command bar
-- that I normally wouldn't be able to do, or just faster.
local id = shared.plugin:PromptForExistingAssetId("Animation")
if id > 0 then
local ks = game:GetService("InsertService"):LoadAsset(id)
ks.Parent = shared.selected
end
And well surprisingly, this doesn’t clear the clipboard at all. It works as it should.
So honestly, the truth is this is probably a relatively easy fix, and would have probably been fixed if the Animation Editor was open source. Empower the community.