Yeah this behaviour has been here for months now. I'm not sure it is a "bug", because it really looks like browser sniffing from WhatsApp side, but Vivaldi should at least be consistent with its behaviour in normal tab, where their user agent is spoofed to make WhatsApp web work. I agree it is quite frustrating to see that the issue in normal tabs has been solved in only a couple of snapshot, while the issue in panel is still here weeks after weeks, since the 2.5 release (not sure of the exact version though). But I know how much dealing with bug priorities is such a hard task! The workaround mentionned by @Komposten should work, it is exactly what I do every day too FYI, the bug number is VB-33103.