Can plot files be copied to another Full Node?

[GeorgePapageorgakis]

I have 2 full nodes with the same public key and I have tried to move some plots from one Full Node to the other Full Node.
I transfered a whole hdd with plots and all played well.
However, when I tried to copy some plots to the other machine these plots were considered invalid when I run them on the other Full Node.

Is there a procedure that has to be followed when copying the plot files? Should I just cut/paste them or something?
I tried to rename them to .tmp to copy them and then back to .plot, seems to work.
What is going on?