When I copy some text that has been transformed with some text-transform CSS property, the copied text does contain the style transformations.
But when I copy some text, I only want to copy its content, and not its CSS styles.
For example, if the title of an article is turned into uppercase with CSS, I don't want to copy/paste uppercase text, but only its source.
I can read in the bug 3429 that the current behaviour is made on purpose: however it turns out to be quite annoying on a daily basis.
*** This bug has been marked as a duplicate of bug 43202 ***