Conversation mode in Exchange mail not working

I like to (automatically) group my email conversations.
It's working on my Passport for all accounts, except my Exchange account.
Strange thing:
On iPhone and Nokia Lumia, with the very same settings, this conversation mode is working flawlessly.
You can imagine my frustration: When even iPhone can do it, it can't be that complicated.
My guess: The provider probably doesn't stick exactly to the Exchange specifications.
Still: iPhone, Lumia and Surface Pro 3 do it just fine.

Any idea, what might be the reason?
Any idea, how maybe solve it?

Works for me???

Did you check if you have conversation mode on?

Sent from my ‪ Passport ‪

Of course conversations are activated ;-)
And like I wrote: It's working for all my other email accounts, so it's definitely active.
It's not working for a single Exchange account.
But conversations for this account work on iPhone and Lumia.

So:
Conversations in general work on my Passport.
And conversations work for this Exchange account on other platforms...
There are not much settings to play around. So, what could be the explanation? After all, even my dumb iPhone does it right :-(

Posted via CB10 on BlackBerry Passport from Germany

By conversation mode, you mean that the emails are grouped according to subject? If so, no issues with my Exchange and Hotmail accounts.

Posted via CB10 on Passport.

Yes, grouping by subject.
I'm on the newest hybrid leak, maybe that's the reason.

Posted via CB10 on BlackBerry Passport from Germany

Odd!

I just was watching Hub, while sending an email from this Exchange account:
While sending, Hub actually did group the 2 mails (the original one and my reply).
After having sent, they still were grouped.
But when clicking on this group, Hub briefly was working and then the 2 mails got separated.

Grouping still flawlessly works for all my other accounts.

And for this Exchange account it still is working for a few other systems (iPhone, Lumia, Surface Pro)...

Posted via CB10 on BlackBerry Passport from Germany