[luatex] hyphenation with multiple \patterns

[David Carlisle]

this came about as a lualatex question on stackexchange but I'm
re-asking here, with a plain tex example

https://tex.stackexchange.com/q/470001/1090

In the file at the end the string babababa has hyphenation points
between each letter in all cases except one, highlighted. It seems
particularly odd that the last three, which all use two \patterns
don't work in the same way?

I couldn't find anything in the manual that would explain this (and I
got lost trying to follow the source:-) so asking here....

David


\parindent0pt
\parskip20pt
\tt
\tracingonline1
\def\test#1{%
\par
\csname newlanguage\endcsname\zz
\language=\zz
\lefthyphenmin=1
\righthyphenmin=1
#1
\detokenize{#1}
\par
\vbox{\hsize1pt
babababababa}
\par}


\test{\patterns{a9b ba}}
\test{\patterns{a9b}}
\test{\patterns{ba a9b}}
\test{\patterns{ba} \patterns{a9b}}% why no hyphens here?
\test{\patterns{ab} \patterns{b9a}}
\test{\patterns{xy} \patterns{a9b}}

\end