LO's prsonal dictionary usage doesn't follow the common model with casing entries: than -> than, Than or THAN are valid Marek -> Marek and MAREK UNIX -> UNIX LaTeX -> LaTeX Right now, only exact casing is considered valid. For example "Than" is invalid when "than" present.
well, this is not really a bug, this is the way it is designed. If alterative spellings shall be allowed, you can just add them.
*** This bug has been marked as a duplicate of bug 37954 ***