Multicols environment doesn't work for choicescustom (Bug #342)

%% LyX 2.2.3 created this file.  For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[12pt,english]{article}
\usepackage[scaled=0.92]{helvet}
\renewcommand{\familydefault}{\sfdefault}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage[landscape,letterpaper]{geometry}
\geometry{verbose}
\setcounter{secnumdepth}{2}
\setcounter{tocdepth}{2}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[authoryear]{natbib}

\makeatletter
\@ifundefined{date}{}{\date{}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands.
\usepackage[insidebox,separateanswersheet,automarks]{automultiplechoice}
\usepackage{multicol}

%%%
%%% Remove paragraph indentation
%%%
\parindent=0pt
\setlength{\parskip}{0.8\baselineskip}
\raggedright

%%%
%%% Set up AMC environment
%%%
\AMCtext{draft}{}
\AMCtext{message}{}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%
%%% begin document
%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\makeatother

\usepackage{babel}
\begin{document}
\newcommand{\course}{303}
\newcommand{\coursechap}{2}

\element{chapter2}{
\begin{question}{Question 2}
Suppose that Jones builds a new house, then she sells it to Smith,
and then Smith sells it to Williams. The total net investment from
these transactions is: 
\begin{multicols}{2}
\begin{choicescustom}
\wrongchoice{zero. }
\correctchoice{1 house. }
\wrongchoice{2 houses. }
\wrongchoice{3 houses.}
\end{choicescustom}
\end{multicols}
\end{question}
}

\element{chapter2}{
\begin{question}{Question 2}
Suppose that Jones builds a new house, then she sells it to Smith,
and then Smith sells it to Williams. The total net investment from
these transactions is: 
\begin{multicols}{2}
\begin{choices}
\wrongchoice{zero. }
\correctchoice{1 house. }
\wrongchoice{2 houses. }
\wrongchoice{3 houses.}
\end{choices}
\end{multicols}
\end{question}
}

\title{ECON \course}
\author{Quiz on Chapter \coursechap{} reading}
\maketitle
\onecopy{1}{
  \insertgroup{chapter\coursechap} 
}
\end{document}

I do a lot more with it to make the slides look like Beamer, and the code is modular so I can swap in different questions easily. I use AMC because I teach multiple sections of this course and I want the quiz to be different (order of questions, order of answers) for each section. I did my best to trim it down to the bare minimum, but I didn't strip out the LyX stuff.

It seems to me that, in the first question, you don't see there is a second column because the 4 answers don't fill the first column.
If you add a paragraph break after each answer for exemple, you will see the second column (add the folowing right after \begin{document}).

\def\AMCanswer#1#2{#1 #2\par}

David Dixon wrote:
But that doesn't explain why it makes two columns with choices but not choicescustom. The \par does work pretty cool, however - but I can't seem to adjust any other vertical spacing when I end with \par.

But that doesn't explain why it makes two columns with choices but not choicescustom.

I think it does make two columns with choicescustom. But if you provide text that does not fill one line of one column, you don't see the second column.

Please send code as attached files (Click on Files just under the text) instead of pasting it in the text.

So what I'm inferring is that choices does something like

   \def\AMCanswer#1#2{#1 #2\par} 

so I have to do something like that in choicescustom to get it to make columns. So in that sense, I concede, user error :)

What I was doing was

  \def\AMCanswer#1#2{\par\choicelabel{#1}\hspace{24bp}\choiceanswer{#2}\vspace*{12bp}}

If I put the \par at the end

  \def\AMCanswer#1#2{\choicelabel{#1}\hspace{24bp}\choiceanswer{#2}\vspace*{12bp}\par}

it doesn't help. It only works if I get rid of the \vspace*{12bp}, but I want that space.

Maybe you can use (with standard choices environment)

\AMCinterIrep=24bp

to add space between answers.
Also, consider using the plain package option (do avoid interferences with AMC layout), and maybe also the pdfform one (with AMC development version)?