Today I discovered that the thread on both my rear hub and freewheel were stripped. I went to my LBS and he told me he's never seen this before. The last time I removed the freewheel was to lightly grease the thread on the hub. There also wasn't the slightest problem when putting the freewheel back on. How the heck does this happen?

The wheel is an unknown 36H 27 inch double wall and the freewheel is a 7 speed Sunrace 13-25. I bought the wheel late september and the freewheel late october.