It can happen if
you accidentally press "ctrl S" as well on the keyboard.. "Ctrl B" controls
the bold function where-as "Ctrl I" is
italics or you could always
underline something with "Ctrl U".
Ctrl K to add a link
Ctrl P to add a picture
Ctrl Z to "undo"
Ctrl Shift Z to "redo" the Ctrl Z function
These show up when you mouse over the item without clicking on it.