Editing a field value is not possible when that field is bound to a parent data (workaround: edit the root parent data directly)

[HFolkertH]

I can not delete the current value of this date fiels and also can not reset it with the default value.

[renaudpawlak]

Ok, that a more general issue. It's because your date field is bound to the parent. You need to go to the top-level parent to set a default value in the root object. In general default values will not work if your data is bound to the parent. Also, when your data is bound, you cannot edit it. Same here. You need to go to the component holding the root data (maybe a container or a data source) and delete it there.

I know, this is very counter-intuitive, so, I will keep this issue open in order to fix it (probably by supporting default values even if bound to parent).