Every quarterly filing since the May 2013 prospectus for the 2018 notes has stated Tesla's intention to repay the principal of all convertible note issues in Cash:
Since we expect to settle in cash the principal outstanding under the 1.5% Convertible Senior Notes due in 2018, the 0.25% Convertible Senior Notes due in 2019, the 1.25% Convertible Senior Notes due in 2021 and the 2.375% Convertible Senior Notes due in 2022, we use the treasury stock method when calculating their potential dilutive effect, if any.
However, the only convertible issue that has actually been settled is the 2018 Notes, and somehow stock was used for much of those recent settlements:
"In the second quarter of 2017, $144.8 million in aggregate principal amount of the 2018 Notes were exchanged for 1,163,442 shares of our common stock (see Note 14, Common Stock ). As a result, we recognized a loss on debt extinguishment of $1.1 million.
In the third quarter of 2017, $42.7 million in aggregate principal amount of the 2018 Notes were exchanged or converted for 250,198 shares of our common stock (see Note 12, Common Stock) and $32.7 million in cash. As a result, we recognized a loss on debt extinguishment of $0.3 million.
In the fourth quarter of 2017, $12.0 million in aggregate principal amount of the 2018 Notes were exchanged or converted for 96,634shares of our common stock (see Note 14, Common Stock). As a result, we recognized a loss on debt extinguishment of $0.1 million
It's akin to Lucy yanking the football away at the last second: perpetually and totally unexpected.