How do I populate a multivalue input with itself during a drilldown?

[thisissplunk]

I have a few inputs at the top of my dashboard, one being a multivalue input. Its default is two values, but I often only have one value in there to filter the result show I'd like.

I then click on a field value in a random panel that reloads the dashboard page with the new selected data filtering the entire dashboard. However, this resets the multivalue input back to default. This is not what I want. I've tried this and it places values into the multivalue input instead, but incorrectly so, returning no results:

 <link field="filename">
            <![CDATA[
              /app/Splunk_Files_App/filedata_dashboard?form.filename=$click.value2$&form.index=$index$&form.filetype=$filetype$
            ]]>
 </link>

The problem is the multivalue $filetype$. It literally populates it with "file_type=exe" when I drilldown instead of "EXE".
Here is the multivalue input if needed:

<input type="multiselect" token="filetype" searchWhenChanged="true">
  <label>File name</label>
  <choice value="*">All</choice>
  <default>EXE,PDF</default>
  <search>
    <query>index=$index$ sourcetype=file_data | dedup file_type | table file_type</query>
    <earliest>$time.earliest$</earliest>
    <latest>$time.latest$</latest>
  </search>
  <fieldForLabel>file_type</fieldForLabel>
  <fieldForValue>file_type</fieldForValue>
  <!--      Build multi-selection search: 
  EX: (sourcetype ="value1" OR sourcetype ="value2" OR ...)
  -->
  <prefix>(</prefix>
  <valuePrefix>file_type="</valuePrefix>
  <valueSuffix>"</valueSuffix>
  <delimiter> OR </delimiter>
  <suffix>)</suffix>
</input>

tldr: I try to populate a multivalue input with itself during a drilldown and it doesn't work as expected. How do I do this?

[somesoni2]

Try something like this (run anywhere example). See how the multiselect values are formatted (just with delimiter) and how they are used in the search (using subsearch to generate field=value1 OR field=value2... format)

<form>
  <label>Multiselect Dropdown</label>
  <fieldset submitButton="false">
    <input type="multiselect" token="sourcetype" searchWhenChanged="true">
      <label>Source Types</label>
      <choice value="splunkd">splunkd</choice>
      <choice value="splunk_web_access">splunk_web_access</choice>
      <choice value="scheduler">scheduler</choice>
      <default>splunkd,splunk_web_access</default>
      <delimiter>,</delimiter>
    </input>
  </fieldset>
  <row>
    <panel>
      <chart>
        <title>Sourcetype Distribution</title>
        <search>
          <query>index=_internal [| gentimes start=-1 | eval sourcetype="$sourcetype$" | table sourcetype | makemv sourcetype delim="," | mvexpand sourcetype ]| timechart count by sourcetype</query>
          <earliest>-60m@m</earliest>
          <latest>now</latest>
        </search>
        <option name="charting.chart">line</option>

        <option name="charting.legend.placement">right</option>
        <drilldown>
          <link>
            <![CDATA[
               /app/search/multiselect_dropdown?form.sourcetype=$click.name2$
             ]]>
          </link>
        </drilldown>        
      </chart>
    </panel>
  </row>
</form>