I've been sitting studing configurator and i think i have it figured out?
I've enclosed screenshots to help.
The "\" doesn't seem to be programed as active in any layer? in the screenshots : the area under the heading "all other layers show this."
When the keys look like that in configurator that means that they are un-assigned, look at the differance in appearance with those that have an assignment.
So although it looks like the "\" is available it isn't?
All the keys behave at all layers as they appear in configurator, and all keys seem to be present and correct.
I have added the "\" key ("|" with Shift) to the L10 key on the 'important stuff' layer so that it is always availble.
My needs for muliple and complicated layers is minimal as i do not do overly technical things anyway so this is satisfactory result.