In version 1.2.3, an observer releases a pulse 2 tics after it was pushed(3 tics for the push). releasing a pulse 2 tics later than an observer that was not pushed.
-observers have 2 tic delay
http://gfycat.com/RingedKlutzyDoctorfish

However, in beta 1.2.5.15, an observer pushed by a piston(which takes 1 tic less to extend as of beta 1.2.5) releases a pulse at the same time a an observer that was not pushed despite that observers had a +1 tic delay ever since the update.
https://gfycat.com/RightRichBigmouthbass

Notes:
-When tested in beta 1.2.5, the observer pushed(pistons currently have 2 tic extension) had released a pulse 1 tic after it was pushed. 1 tic later than the observer that was not pushed.
-so in 1.2.3:
it should be 3 tics for the piston + 2 for the observer for a pulse, but the pulse is given after 4 tics instead of 5.
in 1.2.5:
It's 2 tics for the extension +2 tics for the observer, but a pulse was given after 3 tics instead of 4.
in 1.2.5.15
It's 2 tics for the extension +3 tics for the observer, but a pulse was given after 3 tics instead of 5