Light Level in F3 Menu always 0 on Soul Sand

When walking on soul sand in 1.16.1, the 'client light' and 'server light' parameters in the debug menu are stuck at 0; even when right next to a sea lantern. It shows a more normal value (ie 14/15) when I stand on any other adjacent block. This could become an issue when deciding whether an area was available for mob spawns.