Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: white rubber piece on the top lid slides out when using it for hot beverage

I bought the thermos element 5 22 ounce beverage bottle from amazon last week, there is a problem with the small white rubber piece that is mounted on the top part of the lid that aligns itself with the bottle opening, after keeping hot water in it for 15 minutes the piece just slides right in side the bottle making the lid ineffective, not only does it let all the heat scape but if the bottle is inside my back pack it gets leaked and make the backpack all wet! what can I do about that? thats a serious problem.