Re - I've noticed there is a drop down menu box just above the "Load From" bar that always reads "Default workspace" and it's drop down arrow is always greyed out. Is this part of the problem or am I missing some other setting?
Its greyed out in deluxe, in Pro uses have an option to change to an LTE (AutoCAD lookalike) interface, but its not available to deluxe users.
I just tried in deluxe and my settings get remembered, BUT I don't use "last window layout" and "last working file, so can't say if these cause any problems, are you are you logging / using the computer as admin, or different users, the config you saved is probably in (default windows 10 location) C:\Users\your name\Documents\TurboCAD 2017 Deluxe x64\Config, but as far as I know (I may be corrected) this is really like you personal config backup, the ones TC uses to start are in C:\Users\your name\AppData\Roaming\IMSIDesign\TurboCAD 2017\Deluxe x64\Profiles\Built-In (again this is a winows 10 location), they are in 4 files, if there is any problem with TC accessing or writing to that folder it will load default values.
You could check the dates on the files in the 'built in' folder and see if TC is writing to them, lastwl, current.cml, desktop.ist, tc xml.ini. or if you didn't install as admin, maybe just try right-clicking the TC Icon and choose run as admin (assuming you are admin).