The "Timing" section of the ObsTAP search screen has what seems to be an update-trigger bug.
When "Time of Observation: Overlapping specified range" is selected from the menu, and "UTC date/times" is selected with the resulting radio button, data entry fields for times in human-readable calendar formats are displayed. Beneath the fields, normalized date/time values in ISO format and in MJD are displayed.
These displays update correctly when the data-entry fields are edited directly, but when the provided calendar widgets are used to update the dates, while the selections in the widgets are reflected in the data-entry fields themselves, the displays below the fields, including, importantly, the MJD, are not updated.
See the screenshot for the resulting inconsistent state. The result does not change when the calendar widget dialog is closed.
The actual search is still apparently generated correctly if launched from this inconsistent state. This can be verified by looking at the MJD values in the resulting ADQL.