[resolved][BUG] JS exception after upgrading to 5.5.1.0

Uncaught TypeError: Cannot read property 'indexOf' of undefined
    at Object.maybe_format_gradient (deps.js:1)
    at Object.group_to_css (deps.js:1)
    at Object.modify_item (deps.js:1)
    at Object.run_callbacks (deps.js:1)
    at Object.run (deps.js:1)
    at Object.run (deps.js:1)
    at Object.run (deps.js:1)
    at Object.run (deps.js:1)
    at Object.compile_non_compiled_selectors (microthemer.js:1)
    at Object.ensure_backwards_compat (microthemer.js:1)

This happens immediately after I open the MT editing interface. I did some debugging and I think it chokes on a CSS custom code that contains CSS comments (“/* … */”) in the selector. I think the problematic selector is:

.dde_material-shadow, .dde_material-shadow-raise {
	box-shadow: 0 1px 3px rgba(0,0,0,0.12),
                                0 1px 2px rgba(0,0,0,0.24);
	/*box-shadow: 0 3px 6px rgba(0,0,0,0.16),
                                   0 3px 6px rgba(0,0,0,0.23);*/
}

I have to switch back to 5.2.6, remove the comments and then upgrade again and then it works.

PS: this is my internal dev env so I cannot provide you with a link unfortunately.