Modal background staying grey when back button is pressed

[wil93]

as reported here https://forum.cms.di.unipi.it/t/confusione-di-alcuni-tag-e-piccolo-bug/4523

[lucach]

Calling $('.modal-backdrop').remove(); when window.popstate [1] is fired should suffice to solve this.

[1] = https://developer.mozilla.org/it/docs/Web/Events/popstate