I know this is a TinyMCE issue but perhaps it could be fixed anyway. When pasting content into a message, if ctrl+z/undo is then used the expected behaviour would be to remove the pasted content. In reality, the entire line of text on which the pasted content resides is removed, sometimes resulting in complete loss of a post. As so much text is pasted with unexpected formatting in TinyMCE, undo directly after pasting has become a fairly automatic move. Due to this, I experience this issue on a pretty much daily basis on XenForo forums.