I rarely, if ever, have had "Isophotes" toggled on, but today I wanted
to do it but they don't happen on the Display -> Isophotes toggle. I
have tried:

* CD-ROM in drive
* Resetting to Factory Defaults
* Installing the toolbar button and toggling it via that

Over months of playing, I've probably changed something else that's
affected it -- any bright ideas anyone?

TIA
--
Stephen Tonkin