The conflict issue may be better explained by this:
For instance, let's say you have a forum format like so:
[forum_title]-[forum_id]/
And a thread format like so:
[thread_title]/
As far as DBSEO is concerned, the two URLs look like so:
<any character or symbol>-<a number>
<any character or symbol>
Now let's assume someone posts a thread title like so:
New Release: DBSEO version 2
The rewritten URL for that thread would, without the -a suffix, be:
new-release-dbseo-2
Notice how this matches the <any character or symbol>-<a number> rule for forum URLs? In other words, if forum URLs are given a higher "priority" than thread URLs, the rewritten URL would be resolved as if it was a forum, and when visiting that thread you would see forum ID 2 (or an error message, if that forum ID does not exist or is inaccessible).
However, with the rewritten URL including the -a suffix, the URL for that thread would be:
new-release-dbseo-2-a
Notice how it no longer matches the <any character or symbol>-<a number> rule for forum URLs? There is now a character after the number, which means it can't be a forum URL.
This is a very simplified example, but it demonstrates why it's vitally important to make sure that URL formats can be resolved as accurately as possible.
That's a canned response to whenever we get someone asking for why there's an -a in certain titles, but the same principle applies - the title and ID variables still resolve the same way in this case.