It may be a defect, but the lock is half-decent so it isn't a major defect

Like the lock on the cap which does a great job of keeping the water in without spilling

A twist-top lock mechanism prevents leaks when the bottle is not being used

I got this bottle and another brand with a much more convenient push/pull lock

As for the top lock, it is a good design to lock and unlock.

Leak proof, even when the twist top isn't set to 'lock', and it keeps my water cold for about an hour.

A twist-top lock mechanism prevents leaks when the bottle is not being used

The lock is brilliant, overall, whoever designed this thing got it

Easy twist lock

I like having a lock