custom permalink not saved

When creating a custom permalink structure /%postname%/ the highlight reverts back to the Post Name setting when pressing save.

I assume as the highlight changes to another setting that the custom setting is not saved, is that correct?

HOWEVER if I change to /%postname% with no backslash the highlight for custom setting remains on custom settings, so I assume this indicates that this setting is now saved.

I know /%postname% is incorrect syntax but I’m confused as to why the correct syntax /%postname%/ with backslash doesn’t appear to be saved.

Using WP version 3.3.1, HeatMap Theme Pro 5.2 and have tried with Twenty Eleven 1.3 theme but no improvement.

Help would be greatly appreciated!