Actually this appears to not be working in the latest version - When you do this and click "edit ticket", make an edit and submit, the page goes white.  The changes are made, but it doesn't load the "thread" page again :-/

We have the same issue.

2 months later

+1 for this feature, I think for many users this would be extremely useful because closed tickets are sometimes required for reference and the workaround of creating a separate department is not really ideal.

4 months later

The patch proposed by fearless worked fine on 1.9.9 but the closed counter still shows 0. I also confirm the problem when you try to save edits. It gave a server error 500.

4 months later

Same problem in v1.10-rc.2 (231f11e).I believe it's natural for Agents to look back for older tickets if needed. We have returning customers. This feature could help many times. Br,Dali

Are there any paid custom modifications of osticket available? Of course I don’t mind the feature is used publicly after being paid.

I have a PHP programmer that most likely would fix this, but it that goes overwritten by next update, same problem can happen with every update.

Thank you very much.

Br,Dali

I have not used OSTicket in a while but I tend to agree with some of the comments on here. If a ticket was assigned to someone and closed by that same someone then Access should still be retained. Closed or not.@[deleted] unfortunately there is no way in OSTicket for a mod to be implemented without needed to be re-done upon the next release (yet). The Plugin architecture is at least a cleaner way of implementing mods but fundamentally you are still extending or modifying the core code which is there to make it work. The best way I have been told to try and get this added more permanently into the core code is to edit the code, create a git issue and submit a pull req.

So, a plugin to view old tickets would be appreciated then? I know my next job!

Yes, I would appreciate it greatly!Thank you!

Alright, I've started, written a patch, and infrastructure to manage versioned patches for Admins. Yeah.. Sounds complicated, basically, you get a few checkboxes of which "MOD"s you want to enable, and it keeps track of it in the background and applies and reverts the patches whenever you enable/disable the MOD. I keep referring to them as MOD, because they do actually Modify core, however they are encapsulated within a Plugin, so should be relatively version safe. :-)I'll get it thoroughly tested and play with it some more, but I thought you should know progress is being made.Checkout the idea here: https://github.com/clonemeagain/osticket-mod-to-plugin/blob/master/mods/EnableClosedTicketsView.1.9.patch (Used the above code to write a patch, and the surrounding plugin manages the patch). 

3 years later

For osTicket (v1.11.0-rc1) you can change the following file: include/class.staff.php
method: getTicketsVisibility()
line:

$visibility = Q::any(new Q(array('status__state'=>'open', $assigned)));
to 
$visibility = Q::any(new Q(array('status__state__in'=>array('open', 'closed'), $assigned)));
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