Setting variable with ISO date is saved as null (UI)

[DHFW]

When I enter an ISO date value like 2023-03-22T13:47:40.174Z variable in the dev-interface UI, it is not saved. When I get the variable replaced in my mock file (after actually calling the mock response, the variable value is replaced with null.

Dev interface version: 3.2.1.

Note: when setting the value via api, the value is correctly replaced, so the issue is only present in the front end/UI.
Note2: we set the value in the API with (new Date()).toJSON() which results in '2023-03-22T13:47:40.174Z'