Try to change from
Code:
<idx:entry>
<idx:orth>bring<idx:infl><idx:iform value="brought"/></idx:infl></idx:orth>
<br />
<span color="navy">bringen</span>
</idx:entry>
to
Code:
<idx:entry>
<idx:orth>bring</idx:orth>
<idx:orth value="brought"/>
<br />
<span color="navy">bringen</span>
</idx:entry>