Buckler not providing PRR with (Greater) Shield Mastery?

[wax_on_wax_off]

So just noticed that it appears that I'm not getting any PRR when equipping a buckler even though I have Greater Shield Mastery on my Swashbuckler.

Anyone had experience with this? Known issue?

Naked PRR is 11 which I'm uncertain of its origin as I unequipped everything.

I tested:
Nothing = 11 PRR
Large Shield = 11+25 PRR (+10 base +15 Greater Shield Mastery = WAI)
Buckler + Sceptor = 11+0 PRR
Buckler + Handaxe (grants single weapon fighting bonuses) = 11+0 PRR
Buckler + Handaxe with Swashbuckling activated = 11+0 PRR
Quarterstaff = 11 PRR (so presumably not from Shield Mastery feats)

Thoughts?

[wax_on_wax_off]

Regarding naked PRR of 11:
3 from Past Life: PDK

Not sure where the other 8 is coming from.

Is it possible it is from Shield Mastery Feats?
Perhaps:
1. Greater Shield Mastery is only providing 8 PRR but all of the time.
2. Perhaps Shield Mastery and Improved Shield Mastery are stacking (3+5=8) and GSM is providing nothing.