As the title says, in the current snapshot with experimental redstone features on, Observers do not detect a change in redstone dust when it becomes powered or unpowered. Observers still detect when dust has been placed in front of them and when the direction of the dust has been changed, but they do not detect the powered state, which is a major issue.

Steps to reproduce:
1. Enable the experimental Redstone Dust features

2. Create any sort of redstone circuit configuration that involves an Observer facing a piece of Redstone Dust (example image)

3. Attempt to make Observer send a signal when the dust has been powered or unpowered (In this example, attempt to make the Copper Bulb turn on when the Lever is activated)

Observed Result
The Observer does not send a signal (in this example, Copper Bulb should be on)

Expected Result
The Observer should send a signal (activating the Copper Bulb)