Since at least version 5.0 a fresh installation of Libo includes GB-eng and SL dictionaries as available (Options|Language Settings|Writing aids|user-defined directories), although the concerned language selection has not been chosen.
These dictionaries appear as default in the share directory of the program:
C:\Program Files\LibreOffice 3.6\share\wordbook
and have to be deleted to get rid off of them.
This is probably a "Linguistic" issue, therefore changed component accordingly.
*** This bug has been marked as a duplicate of bug 50827 ***