Media upload doesn’t work with AJAX editor

[thefuxia]

When media uploads are enabled in the AJAX Editor, the upload button is visible, but clicking it raises just an error:

Uncaught exception: TypeError: Cannot convert 'n' to object
Error thrown at line 595, column 2 in <anonymous function: w.template>(n, t, r):
    n.replace(u, function(t, r, e, u, o) {
called from line 27, column 3 in <anonymous function>(data):
    compiled = compiled || _.template( $( '#tmpl-' + id ).html(), , options );
called from line 2939, column 3 in <anonymous function: css>():
    media.view.Attachments.$head().append( this.cssTemplate({
called as bound function from line 2924, column 3 in <anonymous function: initialize>():
    this.css();
called via Function.prototype.apply() from line 3521, column 3 in <anonymous function: initialize>():
    return media.view.Attachments.prototype.initialize.apply( this, arguments );
called via Function.prototype.apply() from line 773, column 3 in <anonymous function: a.View>(t):
    this.initialize.apply(this, arguments);
called via Function.prototype.apply() from line 347, column 3 in <anonymous function: constructor>():
    Backbone.View.apply( this, arguments );
called via Function.prototype.apply() from line 880, column 3 in <anonymous function: constructor>(options):
    wp.Backbone.View.apply( this, arguments );
called via Function.prototype.apply() from line 1121, column 5 in <anonymous function: r>():
    return i.apply(this, arguments)
called via Function.prototype.apply() from line 1121, column 5 in <anonymous function: r>():
    return i.apply(this, arguments)

To debug that, I have replaced the minified underscore.js with an unminified version from the original repo (not included in WordPress core for no obvious reasons). The error is now:

Uncaught exception: TypeError: Cannot convert 'text' to object
Error thrown at line 1130, column 4 in <anonymous function: _.template>(text, data, settings):
    text.replace(matcher, function(match, escape, interpolate, evaluate, offset) {
called from line 27, column 3 in <anonymous function>(data):
    compiled = compiled || _.template( $( '#tmpl-' + id ).html(), , options );
called from line 2939, column 3 in <anonymous function: css>():
    media.view.Attachments.$head().append( this.cssTemplate({
called as bound function from line 2924, column 3 in <anonymous function: initialize>():
    this.css();
called via Function.prototype.apply() from line 3521, column 3 in <anonymous function: initialize>():
    return media.view.Attachments.prototype.initialize.apply( this, arguments );
called via Function.prototype.apply() from line 773, column 3 in <anonymous function: a.View>(t):
    this.initialize.apply(this, arguments);
called via Function.prototype.apply() from line 347, column 3 in <anonymous function: constructor>():
    Backbone.View.apply( this, arguments );
called via Function.prototype.apply() from line 880, column 3 in <anonymous function: constructor>(options):
    wp.Backbone.View.apply( this, arguments );
called via Function.prototype.apply() from line 1121, column 5 in <anonymous function: r>():
    return i.apply(this, arguments)
called via Function.prototype.apply() from line 1121, column 5 in <anonymous function: r>():
    return i.apply(this, arguments)