[tex-live] TLU reports "... pdftex paper size = (null)"

[Daniel Branning]

 From the TLU log window:

**********

... Welcome to TeX Live Utility 1.21, running under Mac OS X ...

...

... Unable to determine current paper size for pdftex
... System paper size = letter, pdftex paper size = (null)

...

**********

whereas:

$ > tlmgr pdftex paper
Current pdftex paper size (from 
/usr/local/texlive/2015/texmf-config/tex/generic/config/pdftexconfig.tex): 
letter


Also, `TLU->Configure->Change Paper Size... ->letter->accept' runs the 
same procedure as does:

$ > sudo tlmgr paper letter
/usr/texbin/tlmgr: setting paper size for context to letter.
/usr/texbin/tlmgr: setting paper size for dvipdfmx to letter.
/usr/texbin/tlmgr: setting paper size for dvips to letter.
/usr/texbin/tlmgr: setting paper size for pdftex to letter.
/usr/texbin/tlmgr: setting paper size for psutils to letter.
/usr/texbin/tlmgr: setting paper size for xdvi to letter.
Regenerating all formats, this may take some time ...running fmtutil-sys 
--no-error-if-no-engine=luajittex --all ...

but neither keeps the radio button for "letter" checked after 
completion, nor saves the settings for pdftex, apparently.

Thanks,
-daniel