Kubrick shot his last three films open matte, but always intended them to be shown 1.85:1 theatrically. In 1991, when he approved new digital transfers of all his films for laserdisc, he opted to have his films unmatted whenever possible. Given the low resolution of laserdisc and the unavailability of 16x9 enhancement, he didn't like how the matting wasted so much of the picture when there's perfectly safe image underneath. However, there's no reason to keep them unmatted now that we have high resolution 16x9 DVDs and also high-def formats. His storyboards for The Shining had marks showing that the images were to be composed for 1.85:1 first, but also made safe for 1.33:1 in the event of mattes not being added.

Just a rundown of official aspect ratios for his films:

Killer's Kiss - 1.37:1
The Killing - 1.75:1
Paths of Glory - 1.85:1
Spartacus - 2.20:1 (or 2.35:1 on 35mm prints)
Lolita - 1.66:1
Dr. Strangelove - 1.66:1
2001: A Space Odyssey - 2.20:1
A Clockwork Orange - 1.66:1
Barry Lyndon - 1.66:1
The Shining - 1.85:1
Full Metal Jacket - 1.85:1
Eyes Wide Shut - 1.85:1