I don’t think the original poster described the problem precisely enough. This is an issue for me, so let me be specific.
Let’s say I have a Calc spreadsheet with a cell that contains “one two three”. In WIndows, if I copy from that cell and paste it into a single-line edit control in another app, I get “one two three” and nothing else. Perfect.
But if I perform that same operation on Linux, what the app gets is “one two three\n”. There is a newline appended to the string. You don’t actually see “\n”, of course, you see whatever U+000A happens to display in whatever font is being used. In my case, it’s the square box with 000A laid out in a 2x2 grid.
Clipboard handling in X has always been problematic. It’s not impossible that this is a Linux problem, but it is a problem.