Hi Richard, kristianb, Philipp ...,
just want to tell you, that this problem is solved for me (at the moment)!
I did not changed anything with regard to the files. Only thing I did was of course update boxcryptor regulary and update windows. So maybe that fixed this "bug".
Anyway, it was working with windows 8.1. the whole last year for me. then suddenly I could not add the boxcryptor drive in the windows indexing options any more. This weekend I tried I realized that it is now possible again.
Finally I can add the decrypted boxcryptor-files to the windows-search-index again.
If I can provide some more information, which might help the boxcryptor-support - please let me know. Probably Microsoft fixed that issue during one of the last windows updates :-)