I can reproduce this issue, but I'm not sure what GrapheneOS can or should do about it. Vanadium is a hardened variant of Chromium, so a lot of what we see or experience is inherited from the upstream Chromium project. I don't think that GrapheneOS has made any changes to this feature, so it's almost certainly an upstream bug. It wouldn't be surprising if other browsers have the same issue, like Edge, Brave, or even Google Chrome.