I've been noticing this for awhile now, but when you copy and past these days you are really copying everything, the link, format and browser pending, even the highlight on the text.
I'm not sure why stuff is copied with website text formating. I think it has to do with CSS, and HTML codes being copied as well.
There is an Add-on for Firefox called Copy As Plain Text which makes it possible to copy text without the website formating by picking Copy as Plain Text from the right click menu for the mouse.
Google Chrome has an option in the right click menu to copy text as plain text.
You can also copy your text in notepad, and copy the text you copied to Notepad which removes the weird formats because all text in Notepad gets converted to plain text after you pasted it to Notepad.
