Probably not the case with 2.6.3, but haven't tested. Currently there is a weird bug. If one has Preferences > Group chat > "Show chat roles icons instead of presence icons" enabled, everything is fine. But if you have this disabled, it should show presence bubbles in the list instead of role icons. It won't show any icon and even your own icon if you are just a visitor or a member of the room. It only shows participants if you are at least admin. Works fine on other clients.
This is related to "Broadcast presence for:" setting in the room's settings. If you are a member, then your icon will at least show up if only Moderator or Visitor are selected (but only your presence icon). If you are removed from members (and became simple Participant i think), then your icon will only show up if Participant is checked in that setting. I can't understand how this setting is supposed to work now and what it means. Thought that presence should only be shown to selected roles and if every role is selected then it should be shown to everyone. Then this logic in Spark is broken.
UPDATE: When Show Real JIDs of Occupants to: is set to Anyone, then it shows presence icons no matter what Broadcast presence for setting is.