Does anyone have a suggestion on how to workaround this fault in steam?

I just discovered that steam has started installing games to -
C:\Program Files (x86)\Steam\steamapps\common
and not to
C:\SteamLibrary

I can't figure out how to stop it.

Steam appears to be unaware that C:\SteamLibrary exists - sometimes but not always.

If I try to add C:\steamlibrary as a new installation drive it says you already have a C:\steamlibrary
So why don't you recognise it?

If I manually add a new folder SL2 to c: and then try to get steam to recognise it, steam rejects the selection saying I already have a steamlibrary on c:

So what's the technical problem having 2 libraries on the one drive? Absolutely nothing if it's programmed correctly.

Lastly, as a former manager of business critical systems in a global telco, my view is that installing games to program files directories is very poor practice.