Changes have been made in Git for this ticket:

Bug #10302: Comparing 2 objects won't work properly if internal 
variables have changed

  5 files changed, 22 insertions(+), 8 deletions(-)
http://git.horde.org/horde-git/-/commit/6e93a8ccda4f66db3eb0fa4f243d321c95ba7a09

Some rudimentary debugging in message.php line 573:
if ($conf['spam']['reporting'] &&
     ($conf['spam']['spamfolder'] ||
      ($mailbox != IMP_Mailbox::getPref('spam_folder')))) {
...
}

That conditional is being resolved to true when I view a message in my 
spam folder, specifically ($mailbox != 
IMP_Mailbox::getPref('spam_folder')) is true. Here are the logs I had 
it print out.

HORDE [imp] message.php - report as spam [pid 1681 on line 577 of 
"/usr/local/www/apache22/horde/imp/message.php"]
HORDE [imp] IMP_Mailbox Object (     [cache] => Array         (         
      [n] => Array                 (                     [0] => .       
                [4] => 1                 )              [d] => 1       
       [ro] =>              [a] =>          )      [changed] => 0     
[_mbox:protected] => Spam )  [pid 1681 on line 578 of 
"/usr/local/www/apache22/horde/imp/message.php"]
HORDE [imp] IMP_Mailbox Object (     [cache] => Array         (         
      [n] => Array                 (                     [0] => .       
                [4] => 1                 )              [d] => 1       
       [ro] =>              [a] =>          )      [changed] => 1     
[_mbox:protected] => Spam )  [pid 1681 on line 579 of 
"/usr/local/www/apache22/horde/imp/message.php"]

The first IMP_Mailbox Object is $mailbox. The second is 
IMP_Mailbox::getPref('spam_folder'). 
IMP_Mailbox::getPref('spam_folder') has changed = 1. $mailbox has 
changed = 0. Not sure what changed means in this context, but I hope 
this helps. I'm using dovecot 2.0.12 as my imap server, by the way, if 
this issue is related to the imap server giving us some unexpected 
results.

Here is the attachment.

It is happening on both my production and test machines. "Report as 
Innocent" correctly shows up in the list view of messages, but when 
reading a message in the Spam folder, it switches to "Report as Spam" 
and if I click that link it follows through with reporting it as spam. 
Its not as if the link is being mislabeled. In my mail/imp 
preferences, I have the spam folder correctly set. I'll try to debug 
it a bit further and see if I can give you guys more information. 
Here's the versions I'm running if that helps:

Address Book (turba) 3.0.3
Filters (ingo) 2.0.2
Horde (horde) 4.0.6
Mail (imp) 5.0.7

I'm now attaching a new screenshot from DIMP. My original bug report 
was solely based on the imp traditional view. Dimp is showing both 
Spam and Innocent buttons when I read a message in my spam folder.

I don't see this - it correctly shows "Report as Innocent" for me.

When I am in my spam folder, the Report as Innocent link shows up as 
expected. However, if I click on a message in the Spam folder to view 
it, I get a Report as Spam link instead. This is within the IMP 
traditional view. I attached a screenshot. Notice the report as spam 
link even though I am in my spam folder.

Relevant IMP configuration:
$conf['spam']['spamfolder'] = false;
$conf['spam']['program'] = '/usr/local/bin/sa-learn --no-sync --spam';
$conf['spam']['reporting'] = true;
$conf['notspam']['spamfolder'] = true;
$conf['notspam']['program'] = '/usr/local/bin/sa-learn --no-sync --ham';
$conf['notspam']['reporting'] = true;