The black "show shadow clipping" indicator not extinguishable. What can be done? I tried the obvious. There is no evidence of clipping.

Question

The black "show shadow clipping" indicator not extinguishable. .  What can be done?  I tried the obvious.  There is no evidence of clipping.
Lightroom version: 5.6 [974614]
License type: Perpetual
Operating system: Windows 7 Ultimate Edition
Version: 6.1 [7601]
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 3.3 GHz
Built-in memory: 16364.3 MB
Real memory available to Lightroom: 16364.3 MB
Real memory used by Lightroom: 1055.2 MB (6.4%)
Virtual memory used by Lightroom: 1071.8 MB
Memory cache size: 2.0 MB
Maximum thread count used by Camera Raw: 4
System DPI setting: 96 DPI
Desktop composition enabled: No
Displays: 1) 1920x1080, 2) 1920x1080
Application folder: C:\Program Files\Adobe\Adobe Photoshop Lightroom 5.6
Library Path: C:\Adobe Lightroom Catalogs\2014_05_31 (3).lrcat
Settings Folder: C:\Users\XXXX\AppData\Roaming\Adobe\Lightroom
Installed Plugins:
1) Canon Tether Plugin
2) Facebook
Config.lua flags: None
Adapter #1: Vendor : 1002
  Device : 6739
  Subsystem : 25201462
  Revision : 0
  Video Memory : 1003
AudioDeviceIOBlockSize: 1024
AudioDeviceName: Speakers / Headphones (IDT High Definition Audio CODEC)
AudioDeviceNumberOfChannels: 2
AudioDeviceSampleRate: 44100
Build: Uninitialized
CardID: 26425
Direct2DEnabled: false
GPUDevice: D3D
MaxTexture2DSize: 8192
OGLEnabled: true
Renderer: AMD Radeon HD 6800 Series
ShaderModel: 11.1
Vendor: AMD
VendorID: 4098
Version: 1002:6739:25201462:0000

Answer 1

First off, this image is not a raw image.  It is a compressed small-raw of some sort so Adobe's normal demosaicking algorithms are not being employed, and Adobe is having to reverse engineer R, G, B channels from Y, Cb, Cr channels, so something may be non-optimal this conversion.
Secondly, at least with this non-raw Y, Cb, Cr image, there are some Y pixels that have zero value in the file, so no matter what you do, other than adjusting the bottom of the tone curve above zero, they will be clipped.
It also seems that the clipping indicator triangles are not affected by the Detail settings so turning off any noise-reduction or sharpening is required show you which pixels the clipping triangle is keying off of.
Here is your image opened in an RawDigger which is a raw analysis program that indicates the Y channel does have a minimum value of 0:
Here is a screenshot of LR with a very small crop on the shadowed background area above the performers, with the Detail settings turned off--no noise reduction or sharpening, and the Toning settings as bright as possible, and in that small crop area, there are a few black pixels that are highlighted blue if I turn on the clipping indicator, so it's not surprising, that with this image, at least, the black clipping indicator doesn't turn off very easily.  In this side-by-side, they have the same settings, but the Before image is without the clipping indicator and the After image is with the clipping indicator engaged so you can see the 4 pixels that are 0 in the tiny cropped area:
Here is a DNG of the settings as in the above LR screenshot, other than the embedded preview that appears to be the entire image not the tiny cropped area:
https://dl.dropboxusercontent.com/u/9905000/Dab_143378_smallcrop_maxedtoning.dng