Redstone torches not inverting the redstone signal properly

Verification builds:
1.2.5.15 Retail

Summary:
Redstone torches are not consistently becoming inverting when powered.

Steps to Reproduce:

1. Create a torch burnout clock as pictured here:
   
2. Turn on the lever and observe the torch
3. Break a block above the torch

Observed Results:
The redstone torches are not inverted, and remain on. Breaking the block above them changes their state and they become inverted.

Expected Results:
When the lever is flipped, the redstone torches should be inverted and turn off. Breaking the block above the torch should not make a difference.
Screenshots/Videos attached: Yes

Notes: