Typical scenario: I want to get a snippet from a text file into my terminal (probably running a VIM).
Now I open the file using mousepad, select the snippet, close mousepad, switch to urxvt and hit Shift + Insert to paste the text. (As opposed to non-terminal applications, where the same does the "normal" paste, but let's keep that aside for now).
IIRC, this work-flow used to work perfectly, until a certain moment. Now, since the moment I close the mousepad window, contents of the clipboard is lost, i.e. reverted to that before. Of course I don't want to keep the window open, that only leads to cluttered desktop (= random loss my concentration).
Skip this: Is there any rationale for this? I'm tempted to think that this is some kind of security measure, but frankly, that idea seems so scary to me: I mean, it's supposed to be clipboard, right? Not a VCS nor a password manager, just a plain old simple clipboard. (What next, are we going to have separate cursors in applications? Or separate selections? Or five hands?)
How can I get my old normal clipboard behavior? And by the way, which part of the architecture (X/GTK/Xfce/mousepad) is responsible for this behavior?
After-thought: After reading the first two great answer plus the article linked, I realized that yes, behavior might have changed, but it's more likely that I have misunderstood the clipboards for years, and it's more about changes in my work-flow (i.e. heavy use of vim, ssh and urxvt and keyboard-oriented control) that caused recent increase in my stumbling. (I feel relieved that it's not another instance of terrible trend in FOSS when developers are arbitrarily "improving" fundamentals of desktop tools.)
So while I was expecting a "switch to turn it back" to behave
how it was how I understood it, namely retaining separate "Ctrl+X/C/V" and "MMB", I'll be looking into solutions involving The Grand Unification. Maybe I'll need to tune my work-flow, but at least I'll be understanding my tools.