In previous versions of the game activating a dispenser that had a command block inside would place a command block (allowing for random command block placement).
However, when building some fun command block stuff with the newest snapshot I discovered that this is not the case.
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-80671. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.