My understanding to the relation of "Steady Shot->Auto Shot" is just the same with the relation of pre-TBC "Aim Shot->Auto shot". In the classic "Aim Shot->Auto Shot->Multi Shot->Auto Shot->...." rotation, the Auto Shot hidden cast is delayed during the Aim Shot Cast. The Auto Shot hidden cast will start immediately after the Aim Shot is launched.
I assumes the relation of "Steady Shot->Auto Shot" after Patch 2.3.2 is: When there is 0.5 sec (or shorter than 0.5 sec if we assumes auto shot cast time affected by haste) left from the end of the Auto Shot CD, the Auto Shot hidden cast starts. If a Steady Shot is casting at that moment, the Auto Shot hidden cast will start immediately after the Steady Shot is launched. But from the test results of Test 2 and Test 3, it seems there are two situations:
A) Test 2. /cast !Auto Shot command is sent. Auto Shot hidden cast indeed start immediately after the Steady Shot is launched.
B) Test 3. No /cast !Auto Shot command. Auto Shot is handled by the server. It seems that the Auto Shot hidden cast does not start immediately after the Steady Shot is launched. There is a gap between the moment last Steady Shot launch and the moment the server activate the Auto Shot hidden cast. This gap is where another Steady Shot command can be received and clip the Auto Shot.
I try to explain the above assumptions in the following graph. Green block represents the Auto Shot cd and the yellow block represents the Auto Shot hidden cast. Blue block represents the Steady Shot cast and the Orange block represents GCD.
