Fouga,
Good catch. I rechecked my source and found that the reference was the Flight Safety Training manual dated Dec 94, page 16-82 and it does indeed refer to the 601-3R.
Some folks here still insist on my original response but, until I can quote the source more specifically, I remain uncommitted. Sorry folks for the bad input.
Fouga,
Further to my last, I just reviewed the Flight Safety Training Manual for the 600 dated Aug 86. It does imply that the AP can be engaged on the ground and that, with no modes selected, will lock in the current pitch attitude. It also states that the AP switchlight selector is adjacent to the YD switchlight selector. Not having flown the plane I wonder how difficult it would be to inadvertently select the AP ON vice the YD? In a second scenario, if you were in a hurry and were about to carry out the AP test on the ground (which, as you say, does require the AP to be engaged) it could be possible to be distracted and forget to carry out the test (split check scenario) and continue with the AP engaged. More questions than answers I suppose.