4.4.2 broke my setup

I've just done a straight upgrade to 4.4.2 from 4.4.1 using the same build-config.js file I used before. This has worked fine in the past, but now I'm getting all kinds of odd breakages. I'm using some standard plugins, but loaded externally rather than in the main bundle because I use the editor in some contexts where I want to disable them. For some reason it's ignoring my addExternal commands and is looking for them in the normal plugins folder. It's also 404ing on the moono/skin.js file (which shows in the downloaded script as 'CKEDITOR.skinName = 'moono'), even though I've specified bootstrapck in the builder , and it's visible in the build-config - why doesn't the builder configure that?

I load my own config file after the main ckeditor script, and it contains these critical lines:

CKEDITOR.plugins.addExternal('symbol', '/ckeditorplugins/symbol/', 'plugin.js');
CKEDITOR.plugins.addExternal('codemirror', '/ckeditorplugins/codemirror/', 'plugin.js');
CKEDITOR.plugins.addExternal('smtags', '/ckeditorplugins/smtags/', 'plugin.js');
CKEDITOR.config.extraPlugins = 'symbol,codemirror,smtags';
CKEDITOR.config.skin = 'bootstrapck';

Despite these calls, I get 404s for all three plugins looking in the normal /ckeditor/plugins folder. It's clearly seeing the config.extraPlugins or it wouldn't be looking for them - and if I comment out that line it doesn't look for them. window.CKEDITOR_BASEPATH is showing the correct value.

Again, all this worked fine in 4.4.1... Any idea what's gone wrong?

I've attached my build-config.js file.