See https://en.wikipedia.org/w/index.php?title=User:99of9/sandbox3&oldid=645853719 for reproducible sample, including instructions for reproducing several related problems.
**Steps to reproduce this one:**
1) Open page containing text and a <ref>. This is reproducible in Firefox 35 and Safari 6.2.2 on Mac OS 10.8.5 as well as in the latest Firefox on Windows.
2) Select the sentence.
3) Press Command-C to copy it.
**Result:** The selected text disappears.
**Attempted workaround:**
4) Maybe it Cut the text, rather than just deleting it? Try to paste it back in: Command-V.
**Result:** Nothing happens. The text was not cut.
**Quirky detail:**
1) Open page containing text and a <ref>.
2) Select the sentence.
3) Right-click to open a menu, and choose Copy from the menu.
**Result:** It copies (and pastes) the text correctly.