Mine does the same thing. If it is the UPO lite, which mine is, the divers extension clasp has a defect in that the tabs that should lock it are not there. I have a genuine clasp I plan to replace mine with.
My first was a corded phone mounted in my car (circa 1989)
2nd was Motorola Flip 1st generation
Then went on a series of Nokia phones loving the 8200 series (8210 was the best and still smallest I've had)
Then migrated to a TREO 700
Then BlackBerry land
Now Blackberry 8300 Curve