When using an execute command in a repeating command block on an entity to detect when it is standing on stairs, it works fine, until you close and reopen the world. It causes it to stop working, but when you break and place the stairs back it starts working again. Command used:

 /execute @e ~ ~ ~ detect ~ ~-1 ~ stone_brick_stairs 0 /tp @e[c=1] ~5 ~ ~

Steps to reproduce:
1. Place oak wood stairs under you, facing east
2. /testforblock ~ ~-1 ~ minecraft:oak_stairs 0 should succeed
3. Relog
4. The same command should fail, saying The block at 255, 69, 283 had the data value of 0 (expected: 0)