Why it seems that principles of chemistry are not being applied in this biochemical process?
From the link given by @Kendall

Such a gradient can be maintained because the thylakoid membrane is essentially impermeable to protons.

I think this solves your dilemma of 'why not maintaining equilibrium' totally.

The reason for this difference is that the thylakoid membrane is quite permeable to Cl- and Mg2+. The light-induced transfer of H+ into the thylakoid space is accompanied by the transfer of either Cl- in the same direction or Mg2+ (1 Mg2+ per 2 H+) in the opposite direction. Consequently, electrical neutrality is maintained and no membrane potential is generated.

It precisely shows why electrical equilibrium is not disturbed due to pH disturbance.
Finally:

2 H2O + 2 NADP+ + 10 H+stroma =&gt; O2 + 2NADPH + 12 H+lumen
12 H+lumen + 4 ADP + 4 Pi =&gt; 4 ATP + 12 H+stroma