in the setup of your description, I don’t see why the output would be unexpected. With the following version of your example code I get the attached PDF output.
\setuppapersize[A5]
\definedescription[descr][
headstyle=bold,
style=normal,
% align=flushright,
location=hanging,
width=broad,
margin=1cm
]
\starttext
\startdescr{Para}
This is a shorter item label, and some text that talks about it.
The text is wrapped into a paragraph, with successive lines indented.
This is another paragraph under the "Para" item.
\startdescr{Sub Item}
This is a description of an item which is within the "Para" item.
\stopdescr
\startdescr{Sub Item}
Another Sub Item
\stopdescr
\stopdescr
\startdescr{Short}
A short item that's not part of that really long "Para" item.
\stopdescr
\stoptext
%%% end