Definitely an edge case, and not a big deal, but submitted in the interest of accuracy. After using the map and completing the challenge:

> inv challenge

haiku challenge map
mime army challenge coin

> refresh inv

Updating inventory...
Requests complete.

> inv challenge

mime army challenge coin
Here's the HTML from completing the challenge:

HTML Code:
<table  width=95%  cellspacing=0 cellpadding=0><tr><td style="color: white;" align=center bgcolor=blue><b>The Haiku Dungeon</b></td></tr><tr><td style="padding: 5px; border: 1px solid blue;"><center><table><tr><td>You have completed the Most Extreme Haiku Dungeon Challenge.<p>You now have access to the /haiku chat channel.  Note that this channel is for haiku <i>only</i>, and is aggressively moderated.<p>Use forward slashes to insert line breaks in your posts in /haiku.<p>example: &quot;This is my haiku / I believe it's a good one / but I could be wrong.&quot;<p><center><a href="da.php">Back to the Dungeoneers' Association</a></centeR></td></tr></table>
While I'm here, is there any way to detect completion of this challenge without visiting the quest log?