Regular expressions with positive and negative lookbehind aren't working with edit modes. Negative lookbehind matches everything, positive lookbehind matches nothing. This is very annoying, because some code cannot be highlighted correctly without these constructs.
Example string: "cab bed babe".
matches all b's although it should only match the 2nd and 3rd
matches no b's although it should match the 1st and 4th
Maybe it has something to do with the substitution '<' for '<' ?