Not sure if your issue is the same as my experience. I bought 5 gallons orange buckets with matching lids at home depot and then the very first time I used them to mix glazes in, I snapped to the fact that they are designed to 'snap' in place and stay there. I was probably a pretty funny sight trying to pry the thing open with my hands and the language was pretty colorful. I had to use a tool as Mark mentioned to open them and they are clearly meant to be that way to protect what's inside from spilling out if the bucket fell over. I can certainly see if plaster, paint or some other building material was being stored and moved around on a job site or in truck beds this would be important.
I switched to some blue buckets at Lowes that have a choice of the locking lids and great thin lipped ones that are meant to be snapped into place by hand with little pressure on or off. They work great and I am slowly switching over to these. The other ones I 'fixed' by taking a crowbar and bending out the lid in a couple of spots so they no longer will 'lock' into place when the lid is pushed down. They still have a little snap in them though and your grinding idea may remove all fit.
Now of course if those tip over the glaze will spill out ;-)