This is correct.
There's not really a place to do this in traditional view.  The 
folders list page is inappropriate (that is intended to show the 
canonical view of the mailbox tree on the IMAP server).

Further testing revealed where I might have made a mistake. It seems 
that Spam is a special use folder and it is listed in dynamic mode 
within the same listing as Inbox, Drafts, Sent and possibly Trash. The 
Subfolders of Spam folder are listed among other non-special folders.

This UI feature might be confusing; if folder is considered special 
then it is separated from its subfolders. The traditional mode does 
not seem to do this. Perhaps special use folders should be accessible 
and listed in both lists in dynamic mode.

This bug may be closed. It is more like confusing UI in this case than 
a real bug.

I don't see this either.  Have you tried clearing your browser cache?

IMAP server and version used in the testing:
Cyrus IMAPD 2.4.12

From: /etc/imapd.conf:
altnamespace: yes
unixhierarchysep: yes

I can select and open the mail folder fine on the traditional version. 
No problems there. Imap server in that case works exactly as expected: 
I can open the folder and I can expand the folder tree.

But on Dynamic version it only allows me to expand the folder tree. It 
won't allow me to open the parent folder of the folder tree. Therefore 
I cannot create any imap debug data because the folder tree is just 
expanded and no data is sent to or from imap server.

The folder is shown like this on the imap server response:
C: 5 LIST (SUBSCRIBED) "" (* "Other Users/*" "Shared Folders/*") 
RETURN (SUBSCRIBED)
S: * LIST (\Noinferiors \Subscribed) "/" INBOX
S: * LIST (\Subscribed \HasChildren) "/" Spam
S: * LIST (\Subscribed) "/" Spam/2011
S: 5 OK Completed (0.000 secs 42 calls)

I can examine the Spam/2011 folder:
C: 2 EXAMINE Spam/2011
S: * 3605 EXISTS
S: * 0 RECENT
S: 2 OK [READ-ONLY] Completed

Not true, works perfectly fine on Cyrus.

To further debug this issue, we need details of the IMP -> IMAP/POP 
communication.

To enable debugging, see instructions contained in 
imp/config/backends.php (the 'debug' config parameter).

Debugging should not be enabled on a production server,   Attach/post 
only the portion of the log that directly deals with the problem 
reported (it may be simplest to clear the log file and then perform 
the event that causes the error).

In dynamic/automatic mode if parent folder has subfolders then you can 
only expand the folder to see expanded list subfolders but you cannot 
see any messages under the parent folder. Thus there is no way to 
open/select parent folder if it has subfolders.