Impossible redstone torch clock

This is an impossible clock circuit discovered by @unknown. I'm re-posting it because its original issue [MCPE-11855] is now closed as invalid.

Steps to reproduce:

1. Build a structure shown in

1. and

1. but without the torch on the center block.

2. Put the torch on the center.

3. Two torches on the sides start flashing alternately.

This circuit deviates from the usual redstone mechanics in many ways:

1. Putting a torch on the center block should play no role in the circuit because it has no adjacent redstone dust nor a solid block above. Then what did it do at all? I have no idea.

2. Side blocks with flashing torches have no reason to be powered in this circuit. They are in fact not even weakly-powered. You can confirm this by attaching more torches to them; they will just stay active except for the flashing ones.

3. If you replace the center block with a redstone lamp, the side torches no longer flash but the torch attached to the lamp keeps active. This is strange because lamps are solid and weakly-powered in this case.

An issue reported in MCPE-11906 might have something to do with this. Both are about alternately flashing torches with no apparent reason.