Changes have been made in Git for this ticket:

Ticket #10351: Don't allow nav_poll toggling if locked or nav_poll_all is set

  2 files changed, 7 insertions(+), 2 deletions(-)
http://git.horde.org/horde-git/-/commit/75d60fcbd505edeb55ea19974f10f329a1216eb1

We should disable poll toggling when this preference is active.  But 
that is not a bug per se.

I think I found the cause: I had the option "Poll all folders for new 
mail" in the "Folder display" section enabled. When this is enabled, 
at the start of each session all folders are marked for polling, and 
disabling a folder only lasts for that session.

Perhaps if that option is enabled, the right menu options to 
enable/disable polling shouldn't be present, since the preference 
setting somewhat overrides them.

That's right. I get no notifications of new mail, but they appear in 
the Virtual Inbox. And folders marked for not polling are lost when 
logging out and logging in again.

To make sure I understand it correctly: the unsubscribed folder is 
indeed no longer polled, but still included in the virtual inbox?

I just realized that it might include the folder in a list even if no 
actuall polling is done, and I just checked and it appears that the 
polling is not done, sorry.

As a matter of fact, I cannot find this option in the traditional 
interface. There are options to subscribe/unsubscribe folders, but not 
for checking or not for new messages. I remember this existed in IMP 4.

One thing that I did notice is that it seems that the request isn't 
even honoured. Looking at the response to ajax.php/imp/poll, the 
folder is still listed there, even after selecting it for not being 
checked.

The request to ajax.php/imp/modifyPool is "add=0&mbox=Sent", and it responds

/*-secure-{"response":{"add":0,"mbox":"Sent"},"msgs":[{"charset":"UTF-8","message":"\"Sent\" mailbox no longer polled for new 
mail.","flags":[],"type":"horde.success"}]}*/

but I can see "Sent" listed in further reponses to ajax.php/imp/poll

Does it make a difference whether you use the dynamic vs. the 
traditional interface?

Other preferences are stored correctly, only this setting is not.

Do other preferences, that you set, persist?

If I mark a folder as "Do not check for new mail", this is only valid 
for the current session. After logging out and logging in again, that 
setting is lost and the folder is again being checked for new mails.