Calendar Quick View create daylight saving time issue.

We have modified vtiger slightly so that when you click on a Calendar event, either from a Summary page, or from a calendar entry, instead of taking the user away from the page to the full form, we load a popup form showing the Quick View event details. We have noticed that events created for next week (w/c 27/03/23) display in the popup 1hr behind where the event's time was originally saved. If you open the event in the full form, the times are shown correctly. I am assuming this has something to do with the popup not handling the Daylight Saving Time change that will happen on the 26th March where our clocks go 1hour forward for summer.

The full form works OK, but the quick view display does not. If a user make a change to any of the fields in the popup form and saves it without checking the time, then the modified times are saved.

Why are the two forms behaving differently?