The filter menu is only checked by me using EthSim. Please check everything twice and tell me, if it is working properly.

To select a filter.
The ST237, ST255/ST5C uses a vane or an intern filter wheel. If such a camera is used, chose "Filter - ST237/ST255 Vane" or "Filter - ST237/ST255 Intern Filter Wheel" and select a filter.
If you are using a ST7,8,9,10 with a CFW 8 or CFW 6A, use "Filter - CFW 8 / CFW 6A " to select a filter.
If you have attached a filter manually, chose "Filter - Manual".
After selecting a filter, it is shown in the "Filter:" StatusBar.
First position: Intern filter wheel, ST237/ST255. Second position: CFW 8 or CFW 6A. Third position: Manuel selected filter.
At the fourth position the string is shown, which will be stored in the File Header
If you are using different sets of filters, you can use the "Setup" menu items to change the captions.

WinScan will not change to the clear filter automatically when the link is established. Before starting an image, check if the right filter is chosen.
For the CFW 8 or CFW 6A select a filter after starting the program / before taking an image.
To take a dark frame using a ST237/ST255, select "Filter - ST237/ST255 Vane - Opaque "
Don't forget to select a clear (or an other) filter before you take a light frame.