This bug was introduced at:

uthor: Paul Licameli <paul.licameli@gmail.com>  2016-06-25 14:18:23
Committer: Paul Licameli <paul.licameli@audacityteam.org>  2016-06-25 19:14:05
Parent: ae14cb0dbccf9587b7a13f5ddc49c2b27acfec1e (Allow tabbing to the button on the time ruler...)
Child:  9f6eedf6e4415b31d4eb2a65e3845f5d287e7fd1 (Bug682: fix Tab key navigation in Preferences, particulary Keyboard)
Branches: includeWxWidgets, labels, labels2, master, remotes/alex-chapiro/master, remotes/audacity/master, temp
Follows: Audacity-2.1.2
Precedes: 

    Compensate for wxW 3 tab navigation deficiencies on Mac...
    
    ... using char hook event handlers.  We don't need to go the extreme length
    of patching wxWidgets source.

Quick Fixed here:
https://github.com/audacity/audacity/commit/2543eacd9435e43079a584f327674e115449cedc

But with this difference from 2.1.2 behavior, which I hope we agree is an improvement:

After highlight leaves the last label, the selection also becomes empty.

If we don't agree to this change of behavior, I will find a different fix.  As it is, this is the easy one line fix.

The symptom still happens, but now only in the very special case, that you have a point label exactly at 0.

This should also admit a simple fix.

Fixed that special case here:
https://github.com/audacity/audacity/commit/35514b7a3ed3f235a32e5e187d2a363ee24d8860

Tested on W10 audacity-win-rf993f1e-2.1.3-alpha-20-sep-16 
and on Mac El Capitan 285f6dc 21Sep16

Tabbing now tabs to each label (region and point labels) but after tabbing from the final label, rather than cycling throgh to the first label the cursor is instead moved to Time=0 and then the next used of Tab takes you to the first label.  I am unsure if this is expected behavior or not?

(In reply to Peter Sampson from comment #5)
> Tested on W10 audacity-win-rf993f1e-2.1.3-alpha-20-sep-16 
> and on Mac El Capitan 285f6dc 21Sep16
> 
> Tabbing now tabs to each label (region and point labels) but after tabbing
> from the final label, rather than cycling throgh to the first label the
> cursor is instead moved to Time=0 and then the next used of Tab takes you to
> the first label.  I am unsure if this is expected behavior or not?

Discussion on Audacity-quality was of the opinion that it wasn't the desired behaviour, so I've removed the empty selection (cursor) at time zero from the cycle:
https://github.com/audacity/audacity/commit/edb99485da0a5518c8915c0c371b4646e59a0b9c

Tested on Mac El Capitan edb9948 27Oct16

Tests ok with no null slection at time=0.  

Tested both forward next label with Tab and backward to precious label with Shift+Tab - both cycled correctly with no null T=0 selection.

Will test on W10 when the next nightly arrives

Tested on W10 audacity-win-rf296c76-2.1.3-alpha-05-nov-16

Tests ok with no null slection at time=0.  

Tested both forward next label with Tab and backward to precious label with Shift+Tab - both cycled correctly with no null T=0 selection.

OK on Ubuntu 14.04. Also tested overlapped labels and a label having text that goes past the end of the visible project.