Permalinks Issue

I know this has been touched upon several times before but today I enabled permalinks to help with the SEO. Ran into an interesting roadblock…

This will work:

https://www.trademarkwindows.co.uk/portfolios/

this won’t:

https://www.trademarkwindows.co.uk/showroom/

but this will:

https://www.trademarkwindows.co.uk/Showroom/
(note the capital ‘S’ in showroom)

I’ve looked at the database and the custom permalink setting for showroom and it is all lower-case.

I wouldn’t mind so much if the problem was more consistent, in fact it’s wiping out half my pages!

FYI: Host is running Apache