Snap install apparmor error: 'profile has merged rule with conflicting x modifiers'

[Joseph Rushton Wakeling]

Hello folks,

With my LDC snap seemingly sorted, I'm now turning attention to my snap for the 
DUB build system:
https://github.com/WebDrake/dub.snap/pull/1/files

I've been able to get this to build as a classic snap with minimal tweaks (just 
switching `strict` => `classic` confinement and adding

     stage-packages:
     - libconfig9
     - libphobos2-ldc68

... to the `ldc` part.

All builds fine, but when I try to install with

     sudo snap install --classic --dangerous dub_1.1.1_amd64.snap

I get an error message:

-----------------------
error: cannot perform the following tasks:
- Setup snap "dub" (unset) security profiles (cannot setup apparmor for snap 
"dub": cannot load apparmor profile "snap.dub.dub": cannot load apparmor 
profile: exit status 1
apparmor_parser output:
profile has merged rule with conflicting x modifiers
ERROR processing regexs for profile snap.dub.dub, failed to load
)
- Setup snap "dub" (unset) security profiles (cannot load apparmor profile 
"snap.dub.dub": cannot load apparmor profile: exit status 1
apparmor_parser output:
profile has merged rule with conflicting x modifiers
ERROR processing regexs for profile snap.dub.dub, failed to load
)
-----------------------

Can anyone suggest what could be wrong here?  The package builds and installs 
fine with `strict` confinement.

Thanks & best wishes,

     -- Joe