How shoud I properly clear VocabBuilder?

[GriMel]

Hi, guys.
Sometimes I want to clear my vocab.db but I have 2 problems with this. Let me tell you what I do.

For clearing database I use sqlite3 and the following queries

DELETE FROM WORDS;
DELETE FROM LOOKUPS;
UPDATE METADATA SET sscnt = 0 WHERE id in ('WORDS', 'LOOKUPS');
VACUUM;

Everything is OK, the base is empty, but after some time I see that all words, deleted from the base are back. I know, that Amazon stores this base but I didn't know it'll give me back all my words in this case. But it is not the main problem

After a couple of deletions I detected that I can't delete anything anymore.
Sqlite3 gives me the following error.

Error: database disk image is malformed

Question 1: Are my queries correct? Should I add something more?
Question 2: What do I do wrong? Why my database got malformed?

[GriMel]

Hey, guys. Nobody knows how to deal with this?

[Cinisajoy]

It is a Sunday. It is Valentine's Day.
Please have a little patience. I am pretty sure someone will be by tomorrow with an answer.
Note: The guys with all the answers do not get paid but volunteer their time here.