swapon vs GEOM labels

Hi Hackers,

I'm playing with glabel(8) and swapon(8) but found a behavior that
is somewhat puzzling.

I boot main (b88df1e893c4) with an USB memstick plugged. The
memstick is da0 and hold a freebsd-swap partition, da0p1. This
partition was given the `swap` label using `glabel label` (i.e.,
an automatic label, stored somewhere into da0p1, AFAIK).

  # glabel status
        Name  Status  Components
  label/swap     N/A  da0p1

Then I give the whole device the `usbmemstick` label using `glabel
create` (i.e., a manual label, not stored anywhere).

  # glabel create usbmemstick da0
  # glabel status
              Name  Status  Components
        label/swap     N/A  da0p1
  label/usbmemstick    N/A  da0

What puzzle me is what happen when I enable swap:

  # sysctl vm.nswapdev
  vm.nswapdev: 0
  # swapctl -l
  Device:      1024-blocks     Used:
  # dumpon -l
  /dev/null
  # swapon /dev/label/usbmemstickp1
  # glabel status
              Name  Status  Components
  label/usbmemstick    N/A  da0
  # swapoff /dev/label/usbmemstickp1
  # glabel status
              Name  Status  Components
  label/usbmemstick    N/A  da0
        label/swap     N/A  label/usbmemstickp1

While swap is enabled, the `swap` label is no longer available. It
comes back when swap is disabled.

Note that I also tried to enable swap using the automatic label
(i.e., `swap`). In such a case this is the `usbmemstick` label
that vanish. And the label is even not restored on `swapoff`.

Is it the expected behavior? Am I doing something wrong?

Regards,
--
Stéphane Rochoy
O: Stormshield