(Working on fixing it...)

The reason why I did not put all the draw.io js and css files in the repo is because

1. draw.io is a very large repo

and 2) the draw.io people commit a lot (as in more than once a week).

The Phorge extension is basically using these files from the repo: https://github.com/jgraph/drawio/tree/dev/src/main/webapp
That's why I preferred to have the draw.io repo somehow as a sub-project in the extension, to keep the extension small.
The user can choose himself when to update the draw.io repo.
Maybe I should implement the draw.io repo as a submodule ?
I don't know if arc liberate has some update functionality for git submodules?

Celerium also "changes" the js files by means of minification.
I bumped into an issue while working on another extension when you use backticked strings in javascript (T15774).
As the js files in the draw.io repo are all minified, it's difficult to find out if these backticked strings are used somewhere in the draw.io code.
The sub-project method won't change the js files.

I wasn't able to reproduce T15745 either

Also sorry for the late reply: I used to receive emails when my name was mentioned somewhere but I didn't for these ones.
I only noticed about this since you assigned T15781 to me

Well I have worked the entire day on this (and I see your mentioned issues)... main problem is: extension is not working with security.alternate-file-domain. That I have fixed at least for the creation/editing of diagrams. I have changed pretty much and would love to send a diff.

@mturdus Just test this if you like. I think this is a first step in the right direction: D25577