I think I found the problem and have a fix!

Long story short, I modified my helm-completing-read-handlers-alist
and added an entry:
(add-to-list 'helm-completing-read-handlers-alist
    `(org-set-tags-command . helm-org-completing-read-tags)
)

I have all the gory details here:
https://github.com/emacs-helm/helm/issues/2183

Thanks all for your help, hope this helps someone else too :)
--Nate



On Sat, Aug 10, 2019 at 4:01 PM Nathan Neff <nathan.neff@gmail.com> wrote:

>
>
> On Sat, Aug 10, 2019 at 3:44 PM Nathan Neff <nathan.neff@gmail.com> wrote:
>
>> Hello all,
>>
>> I created a VM, installed Emacs 26.2 fresh, and installed various versions
>> of org-mode using the tar.gz files from https://orgmode.org/
>>
>> I replaced org-mode in /usr/share/emacs/26.2/lisp/org with various older
>> versions until I found the version of org-mode that breaks the helm tags
>> completion.
>>
>> I found that the latest version of org where the feature works is
>> Org-mode version 9.1.9.
>>
>
> Oops - my aplogies - I assumed that the org-versions stopped at 9.1.9.  I
> tested Org 9.1.14 which (to
> my knowledge) is the last of the 9.1.X versions, and Org 9.1.14 works
> correctly.
>
> I tested Org version 9.2 and Org version 9.2 is the version that breaks
> the tags functionality
> from Helm.
>
>
>
>> I will spelunk around in the code to see what might have changed the
>> behavior - if anyone has
>> suggestions or doesn't have this problem with an older version of org,
>> please let me know - it could
>> easily be something that I have set incorrectly.
>>
>> Thanks,
>> --Nate
>>
>>
>>
>>
>>
>>
>>
>> On Fri, Aug 9, 2019 at 4:28 PM Nathan Neff <nathan.neff@gmail.com> wrote:
>>
>>> Hello all,
>>>
>>> I'm hitting this problem with Org-mode 9.2.5:
>>> https://groups.google.com/forum/#!topic/emacs-helm/tA6cn6TUdRY
>>>
>>> Problem synopsis:  When I use org-set-tags on a heading
>>> with no tags, Helm gives me the correct prompt w/a list of all my tags.
>>> After I have entered a single tag, then no more Helm suggestions are
>>> offered.  This is the bug, and it was fixed at some point.
>>>
>>> Helm + org-mode *work correctly* when I run emacs using
>>> the elpa/helm-20190726/emacs-helm.sh script which comes with Helm
>>> for debugging purposes.  I notice that the org-version in the *working*
>>> example
>>> is 9.1.9 (which is, I presume) the stock org-mode that comes with Emacs.
>>>
>>> I have reproduced this problem on both Linux and OSX.
>>>
>>> Can anyone suggest a next step to take?
>>>
>>> Thanks,
>>> --Nate
>>>
>>>