The "fast forward" code, designed to let a recurring event calculate itself into a future month window, extrapolating rather than looping through each recurrence, forgot to compensate for DST shift.
The DST shift detection had a bug which was using the wrong variable to track the change, missing it, or counting it multiple times, in different cases. Whether the bug caused an issue depended on exactly what kind of recurrence was set up.
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#1610 - Calendar block not correctly handling DST
Recurring events with a time component may not compensate for a DST shift. E.g. an event started at 2PM, may shift to 3PM.
The "fast forward" code, designed to let a recurring event calculate itself into a future month window, extrapolating rather than looping through each recurrence, forgot to compensate for DST shift.
The DST shift detection had a bug which was using the wrong variable to track the change, missing it, or counting it multiple times, in different cases. Whether the bug caused an issue depended on exactly what kind of recurrence was set up.