The 1.91 release is primarily a patch for the Statistics bluescreen in 1.9.
When playing 1.9, do not open the Game -> Statistics screen. You will get a bluescreen error and lose your progress.
1.91 will be submitted to peer review asap. That is exactly 1 week after 1.9 was submitted.
Whats in 1.91:
1. [Fixed] Game -> Statistics bluescreen.
2. [Added] Pressure Plates (1st cut). Steel Doors (bottom) and C4 will react to pressure plates.
3. [Added] Admins can access infinite system shops even when Finite Resources is on (Creative only).
4. [Fixed] Reinstate Shop Blocks for host on new survival maps (Easy and Normal).
5. [Fixed] Teleport to Marker disabled bug.
6. [Added] Option for Host to set new player spawn items (Creative only).
7. [Added] Option for Host to reset the spawn points for all players who have visited the map. Likely used as a once off to 'fix' problems caused in previous versions allowing players into area's they shouldn't have been allowed into.
8. [Added] Lobby Screen option to convert a Dig Deep or Survival world to a Creative world. This is a one way conversion and cannot be reversed. So if you want a copy of the world in it's original mode, then make a copy of it before converting.
9. [Added] When players join your map, if they had already visited your map previous to the permission redesign, their permissions were set to none. This has been changed so they will be set to the default permissions.
10. [Fixed] The bug that was causing craftable items to be locked on the craft select list in both survival and creative maps has now been fixed. When the update is applied, all maps affected by this will be corrected.
11. [Fixed] Hippie unlock fixed.
12. [Added] You can now see a maps default permissions on the Available Sessions screen, so you don't have to join a world to find out you have no permissions.
13. [Fixed] Player placed Spider eggs not spawning spiders after a save/quit/load.
14. [Fixed] Permission control by multiple local players.
15. [Improved] Ore deposit frequency in Survival and Creative maps.
16. [Added] New Game Mode: Peaceful. Same as Survival but no mobs and no injury.
I'll list any other bugs here that we fix before it's submitted.