F12 nedit works as follows for me
Select text with left mouse Relocate the cursor Paste it back with the centre mouse
I know this work fine, but not the copy (ctl c) and paste (ctl v), from the keyboard, from the menu or from the right mouse. However, cut work !! but not let you paste !!!
But, the expected behavior works file when only one file is open !
Regards.
If the left mouse is pressed to relocate the cursor the selected text is lost. (Unless the text is being pasted from an external source)
Dragging the selected text with the centre mouse will move the text Dragging the selected text with SHIFT/centre mouse will replicate the text
Select text, right mouse menu-copy, relocate cursor with left mouse press, right mouse menu-paste also works
John