Different hyphenation pattern when using oldstyle figures?

The different hyphenation patterns are caused by the more spacious kerning and word spacing of the pplx and pplj font families. Quoting Using common PostScript fonts with LaTeX, p. 4 (emphasis added):

By default, the package mathpazo uses the typeface family ppl as the roman text font family. The option [sc] selects Palatino with real smallcaps (family pplx) insread [sic!]. Correspondingly, the option [osf] selects Palatino with smallcaps and default oldstyle figures (family pplj). Of course, oldstyle figures will be used only in text mode, as opposed to formulas. Using either option is strongly recommended: Beside the real smallcaps, the font families pplx and pplj show further improvements over ppl: Increased word space, enhanced kerning tables, additional ‘dotlessj’ glyph.

The results are very similar when

\usepackage{mathpazo}

alone is used or

\usepackage{mathpazo}
\usepackage{fontspec}
\setmainfont[Numbers={OldStyle,Proportional}]{TeX Gyre Pagella}

is specified. When only

\usepackage[osf]{mathpazo}

is declared, the result is different, because the font, for reasons that I don't know, has rather different font space parameters. With \usepackage[osf]{mathpazo} I get

Interword space: 2.91pt
Interword stretch: 1.75pt
Interword shrink: 0.7pt

while, with \usepackage{mathpazo} the result is

Interword space: 2.5pt
Interword stretch: 1.49998pt
Interword shrink: 0.59998pt

The larger interword space for Old Style Figures MathPaZo clearly accounts for the different result.

I got the table by the code

\noindent Interword space: \the\fontdimen2\font\\
Interword stretch: \the\fontdimen3\font\\
Interword shrink: \the\fontdimen4\font

issued after \begin{document}