Why do dashboard queries sometimes not complete?

[jbrenner]

I have a dashboard where some of the chart queries are modified by the value of a dropdown:

  <fieldset submitButton="false" autoRun="true">
    <input type="dropdown" token="time_window_tok" searchWhenChanged="true">
      <label>Select a Time Window</label>
      <choice value="-1week">Past 7 Days</choice>
      <choice value="-1day">Yesterday</choice>
      <default>Past 7 Days</default>
      <change>
          <condition label="Past 7 Days">
               <set token="bins_tok">7</set>
           </condition>
           <condition label="Yesterday">
               <set token="bins_tok">24</set>
           </condition>
      </change>
    </input>
  </fieldset>

Here is one of the queries (I removed everything extraneous):

index=xyz earliest=$time_window_tok|s$ URI="something"
| timechart partial=false bins=$bins_tok$ dc(IP) as MyResult

Sometimes the chart inside the panel displays fine, and sometimes it never renders.
Usually, when you refresh the browser, it displays correctly.
Is there anything wrong with the way I'm doing this? Is there some attribute I can add to the XML to force the dashboard to wait until the queries are rendered?

Thanks,
Jonathan

[jbrenner]

I just discovered the solution, so I'm going to answer my own question.
The issue has nothing to do with the drop-down, The issue is the use of the "bins" keyword.
When I remove it, the queries always complete.