Why copy and paste (^C, ^V) doesn't work with modal screen?

I have a big screen #1 wich calls a smaller screen #2, if #2 is modal then #1 cannot be selected and it's ok, but I can't copy and paste. And if #2 is not modal then I can copy and paste but #1 can come in front of #2 and it's not ok.

Any solution to use cut and paste with modal screens?

TIA
François