adb backup on Marshmallow - is it different? Device and settings: 


Moto X Play ( Stock 6.0.1), unrooted, USB debugging enabled in developer options and verified using adb devices.  Other USB/ Developer options, as in pic below
Enabled desktop backup password as recommended here adb backup command on non-rooted device creates an empty backup file?
Device not encrypted
No additional user accounts on device ( so the issue here for non-primary users is not pertinent)




Goal: I wanted to take adb backup on Mint Linux (17.3) of my apps (with data if possible) and internal SD using this Full Backup of non-rooted devices as reference 

Problems:


When I key this in terminal 

adb backup -apk -shared -all -nosystem -f moto.ab

I get the prompt "Now unlock your device and confirm the backup operation " in the terminal but nothing happens on the device- I do not see any panel to accept  or enter desk top pass word as in pic below (it's the same if I try -system instead of -nosystem)





The terminal reverts to prompt for next command in a few seconds ( A 0 Kb file is created on the laptop)


Question

Am I doing something wrong or Marshmallow require some extras to take a backup as desired?

Moto devices are said to be "pure Android" so I expect this problem to be prevalent on Nexus devices running latest OS



Edit: Things tried with varying sucesss


Nexus 5 Marshmellow ADB backup problems. Going by this post 



  (....) it appears that adb backup isn’t recognizing the -apk, -nosystem, and -noshared switches. Any idea why? From the command line, if i remove those switch the backup runs


adb backup -all -f moto.ab 


works in the sense that I get the option on panel to enter password back up (problem 1 above overcome) but the file size (105 Mb) shows all apps are not backed up (In comparison using ES File explorer, the size is 2 GB)


I had read somewhere on this site that Helium app is based on adb. Helium Wiki says



  Helium is NOT available to Motorola devices. This is because Motorola phones have a bug that break Android's backup mechanism. Until this is fixed by Motorola, Helium will not work on those Androids (....) Update: Helium is working on the Motorola Droid Turbo.


That obviously explains why it doesn't work on my device was the logical conclusion. This called for experimenting, so I downloaded Chrome extension of Helium and activated it (it needed a little workaround explained here 
)

I selected all apps under Helium and it backed up (less some apps shown as "non backable") with a size of 110 Mb (similar to above experiment) 

So, apparently, my device Moto X play is not the problem !


Tried solution here  ADB backup creates 0-byte file; prompts for current backup password even though I never set one; “Failed to set password” for Desktop backup password recommending escaping spaces between arguments


adb backup -apk\ -shared\ -all\ -nosystem -f moto.ab and got a 0 Kb backup file
Same problem here - this is how I fixed it on my side.
Preparations:
- Samsung Galaxy S5 on Android 6.0.1 (not rooted)
- adb v. 1.0.32 running under Windows 10 command line
- password set on the S5  

I succeeded when using quotes for all switches:
adb backup "-apk -noshared -all -nosystem"
-> will prompt for the password and produce a backup.ab  

To backup single apk using a custom file name:
adb backup -f all_apk_obb.ab "-apk -obb com.estrongs.android.pop"

Seems that the switch handling of adb is a bit weird in the latest releases.
I did that before and my old scripts are not working anymore.