Observers can send a redstone signal through transparent blocks and certain tile entities, as shown in the screenshots, yet solid blocks and other tile entities do not transmit a signal.
Environment
OS: Windows 10 Home 64-bit
CPU: Intel Core i7 @ 1.6 GHz
Mem: 4GB RAM
Java 8 Update 101 (1.8.0_101)
Powering blocks broke in the current snapshot, check the next (upcomming) one to see if anything changed