Updating to a newer dev version of a module using Drush (ignoring point/recommended releases, without trashing version control) [NB This question is off the back of, but separate/further to, an earlier question of mine, here.]

I've been using Drush a good while, but every so often I get stumped. At the moment, I'm really not sure how to go about this.

Scenario: currently, the site uses a dev release, dated way in the past. In the meantime, no point release has been created, but a newer dev release has. So we have something like: 

Reroute Email           6.x-1.x-dev (2010-Sep-27)
Recommended version:    6.x-1.0 (2008-Jul-24)   
Development version:    6.x-1.x-dev (2011-Feb-25) 


Doing drush dl &lt;module&gt;-6.x-1.x-dev overwrites the existing  directory with the latest 1.x dev release. That's fine, but it trashes the .svn folder.

If I do drush upc &lt;module&gt;, it will download the point release (see edit below), which I don't want, but if I do drush upc &lt;module&gt;-6.x-1.x-dev, it just refreshes the update data and then tells me "Specified version already installed" on the relevant line on the output.

So how do I use drush to overwrite the old dev release, getting the new one in its place, without trashing the SVN folder?

EDIT: Actually, in this instance, drush upc &lt;module&gt; downloads the correct version, but I'm pretty sure if the point release was dated like 6.x-1.0 (2011-Jan-24) it would have gotten that one. Anyone want to clarify/correct?
I found your question just now because I had the exact same question. Didn't find an exact answer, but this worked for me: 

#svn rm &lt;module&gt;  
#svn commit -m"removing the module... whatever you want to write"  
#drush dl &lt;module&gt;-6.x-2.x-dev  
#svn add &lt;module&gt;  


For some reason, not doing the commit between the rm and the dl caused a problem with svn. I do not know enough about svn to know why, but would be grateful if someone could elaborate!