Dismax: why is "+term1 term2" equivalent to "+term1"??

[Bill Dueber]

I'm using the dismax handler and don't understand the results I'm getting.
Scouring the archives makes me believe that I am, in fact, the only one who
doesn't get this.

Using dismax search on a single field (title), I would expect that the query

  +notes nature

would be read as "Must include 'notes' in the title field; may also include
'nature' in the title field." What I actually get looks to be equivalent to
just "+notes".

The parsed query looks like so:

 <str name="parsedquery_toString">
  +(+(title:note)~0.01 (title:natur)~0.01) ()
</str>

I've futzed around with mm, to no avail. Which boat am I missing??? How do I
get the functionality I'm shooting for?

Setup info:

<lst name="responseHeader">
 <int name="status">0</int>
 <int name="QTime">2</int>
 <lst name="params">
  <str name="mm">0&lt;0% </str>
  <str name="fl">
      id,title,score
     </str>
  <str name="echoParams">all</str>
  <str name="tie">0.01</str>
  <str name="qf">
       title
     </str>
  <str name="ps">100</str>
  <str name="defType">dismax</str>
  <str name="debugQuery">one</str>
  <str name="indent">on</str>
  <str name="q">+notes nature</str>
  <str name="rows">0</str>
 </lst>
</lst>