Is this light hooked up to the switch ?
If so the behavior you get by turning on the switch is defined by the switch. Some remember the last setting, some come on at 100%, some come on a preset level.
If your switch also supports instant status, it can send an event to Vera, where PLEG can detect it and change the settings of the light to a value that is different then the initial setting.
There will be some flickering as this time is not instantaneous.
If you do not have instant status switches it can be a few minutes before Vera even notices the changes … So any changes to the light setting will be long after the initial switch change.