Another user recently had problems (see Save scene with written name) regarding the file name being reverted without their knowledge. The name isn’t reverted until the file name field is no longer being actively edited. It can be confusing when going from actively editing to pressing the save button. If the file doesn’t already exist, it will use the reverted name which the user won’t know and the dialog immediately closes. At least here @muratmaga was able to notice that it wasn’t using the file name “testing.save” because an “already exists” warning appeared for the reverted file name.