(Sequencer) Suddenly can't paste keys between bones

I was copy-pasting keyframes between bones to have a base for mirroring animation (walk cycle), and then suddenly I can’t paste to different bones anymore. Whichever bone I have selected, the keyframes paste into the original bone they were copied from. Is there any setting for it? How did I change it?

Edit:To be more precise, I’m talking about copy-pasting all the transforms at once. It seems to work one by one, but it worked this way too just a while ago.