People buy GARBAGE fake ICs on E-bay. Maybe failed "sweepings off the floor" from a manufacturer.
Buy a real IC from a local reputable electronic parts distributor.
I just bought a function generator kit based on this IC. Switched it on, works nicely. Swapped the IC for one of the ones I got off eBay, output is garbage!
Looks like they were fake/reject IC's
For reference, they were from this listing...
**broken link removed**