Digging a little deeper i found that the following request's return a 400 error
GET /manager/min/index.php?f=/manager/assets/modext/core/modx.localization.js,/manager/assets/modext/util/utilities.js,/manager/assets/modext/util/datetime.js,/manager/assets/modext/util/uploaddialog.js,/manager/assets/modext/util/fileupload.js,/manager/assets/modext/util/superboxselect.js,/manager/assets/modext/core/modx.component.js,/manager/assets/modext/widgets/core/modx.button.js,/manager/assets/modext/widgets/core/modx.searchbar.js,/manager/assets/modext/widgets/core/modx.panel.js,/manager/assets/modext/widgets/core/modx.tabs.js HTTP/1.1
GET /manager/min/index.php?f=/manager/assets/modext/widgets/core/modx.window.js,/manager/assets/modext/widgets/core/modx.combo.js,/manager/assets/modext/widgets/core/modx.grid.js,/manager/assets/modext/widgets/core/modx.console.js,/manager/assets/modext/widgets/core/modx.portal.js,/manager/assets/modext/widgets/windows.js,/manager/assets/fileapi/FileAPI.js,/manager/assets/modext/util/multiuploaddialog.js,/manager/assets/modext/widgets/core/tree/modx.tree.js,/manager/assets/modext/widgets/core/tree/modx.tree.treeloader.js HTTP/1.1
GET /manager/min/index.php?f=/manager/assets/modext/widgets/modx.treedrop.js,/manager/assets/modext/widgets/core/modx.tree.asynctreenode.js,/manager/assets/modext/widgets/resource/modx.tree.resource.js,/manager/assets/modext/widgets/element/modx.tree.element.js,/manager/assets/modext/widgets/system/modx.tree.directory.js,/manager/assets/modext/widgets/system/modx.panel.filetree.js,/manager/assets/modext/core/modx.view.js,/manager/assets/modext/core/modx.layout.js,/manager/templates/default/js/layout.js HTTP/1.1
GET /manager/min/index.php?f=/manager/assets/modext/widgets/media/browser.js HTTP/1.1