Copy & Pasting from another animate file

Hi,

I am having this issue where I have made two animations in different files and wanted to combine them into one animate file. I thought it was simple enough but coping all layers from one animation file to another but something goes wrong.

Let's say I have "A - piano" & "B - paper flying" animation. I wanted B to go straight after A without any keyframes overlapping. I did this by pasting all the B layers into A but as I play it and reach the B animation part, there are partial parts of dimmed A animation without any B animation showing. 

I played around with visibility and layer orders but didn't seem to help.

Is there a limit of layers I can paste from another file? What am I missing here?

Please help me.