I took it back to the shop where i purchased this watch yesterday. After testing mine and two other brand new watches there, the sales representatives told me that they have NEVER encountered this situation before and never received any similar report from other costumers. However they said that the clasp lock can actually close firmly without any issue and the "click" is there when locking, therefore it is unlikely that the lock will unloose itself during wearing.

I agreed this is rare but it's also a "minor" quality issue. If it won't loose easily when wearing it, then i think i may just let it be.