I think it's best to trust your instincts, but I wanted to let you know that my 17 month old DD is also obsessed with putting on and taking off the lid on water bottles, so much so that we hide them from her because it's just so annoying. She does other things like obsessively bite the fur off her teddy or pull fur of the cat and eat it :/ We're not really worried at this stage, but if your instincts are telling you something is up then I'd go with that.