Hello A.,
If the component or rectangle is empty, it is not necessary to have curly brackets:
rectangle Export {
}
You can suppress them with:
rectangle Export
Then, we obtain the good behavior:
[Click to see on PlantUML server]
It seems that curly brackets must be use normaly if there are sub-elements [package or group], see also on the doc.:
If that can help,
Regards,
Th.