The aftermath of last year's blockbuster Apple v. Samsung patent trial is playing out slowly but acrimoniously, with no signs of settlement on the horizon. There's been a steady drip of developments over the past year that have generally favored Samsung—most notably, US District Judge Lucy Koh's order that a retrial must be held on damages. That retrial could slash Apple's billion-dollar payday by up to $450 million.

Sunday night, Samsung lawyers filed an order just out from the US Patent and Trademark Office (USPTO) that renders invalid one of Apple's key patents, No. 7,844,915, the so-called "pinch to zoom" patent. It's definitely a setback for Apple, which presented "pinch to zoom" at last year's trial as one of the innovations that was ripped off by a wide array of Samsung phones.

This is the second Apple patent in its case against Samsung to be called into question at the Patent Office. Apple's "rubber banding" patent was tentatively overturned in October—but Apple eventually prevailed in getting the key claims found patentable last month.

It will ultimately be up to US District Judge Lucy Koh to decide how seriously to take this new development. Reexams are essentially a separate—and typically slower—path of resolving patent disputes. Patent holders can appeal these cases for years, both with the examiner and with the Board of Patent Appeals. The patent is still enforceable while the reexam process moves forward.

The damages retrial is scheduled for November. Apple also has design patents and trademarks that were found infringed in the case, so those aren't subject to reexams.