[NSW] Granville question re signals

["Chris Downs" <cvdowns@ozemail.com.au>]

I stood at the Sydney end of Granville's platforms 1 & 2 for  half an hour
last night.

Watching OP yo-yos on the up main they were leaving Granville and running
express to Lidcombe.  Four up main signals are visible, Granville up main
starter (1), up main intermediate before Clyde (2), Clyde up main starter
(3) and the following up main signal (4) on the way to Auburn.

When a train leaves Granville on no occassion did sig 1 clear before sig 2.
I assumed sig 1 was being hald at danger by the signaller but continued
observation suggested this wasn't necessarily the case.  Once the train is
well on its way to Auburn the aspects shown at 1=G/Y, 2=G/Y, 3=G/R & 4=R/R.
1 & 2 show the same aspect due to the short distance between 3 & 4.  The
part I don't understand however is that 2 when from G/Y to G/G several
seconds before 1 went from G/Y to G/G every time.  The result was a sequence
of four signals showing G/Y, G/G, G/Y & G/R.

Does anyone know why this is so?

Ta

Chris