Preserve datetimes of incidences created from templates
When the editor applies a template, as identified by the "isTemplate" property, it (usually) does not copy its start/end/due datetimes; it keeps the datetimes set before the template was applied. Unfortunately when the instance is saved it still has the "isTemplate" property, and so when it is edited the editor does not copy its datetimes; the GUI fields are left with default values. Removing the property fixes the bug.