Yes, I've already did strings like that, and it works correctly (not when I'm trying to do multiple statement). I can't remember, where I found it, but it was on MTAWiki 99%, or some resource which was referenced by wiki.
Example:
local insertString = "INSERT INTO `houses`\
(`house_owner_id`, `house_enter_x`, \
`house_enter_y`, `house_enter_z`, `house_enter_rotation`, \
`house_exit_x`, `house_exit_y`, `house_exit_z`, \
`house_exit_world`, `house_exit_dimension`, `house_exit_rotation`, \
`house_interior_type`, `house_base_price`, `house_current_price`) \
VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?);"
Works 100% good, no errors or data corruption in tables.
I didn't knew about this, I'll check. But if the problem in that flag, this is weird, that error by MySQL.
Yes, this is the solution. Thank you very much, I would never have guessed where is the problem.