Drop-down menus for Developer Tools when in "Toggle device toolbar" not displaying next to menu button

[Hawlucha]

Excuse the weird wording for the title. I just wasn't sure how to explain this little issue I have with using the "Toggle device toolbar" feature in Developer Tools. These screenshots do better at what I'm seeing.

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The drop-down menu always appears relative to the Developer Tools window's position and not under the menu buttons as one would expect. For someone doing web development, this can get annoying since I would have to find where the menu is, and then move my mouse to that faraway menu that could be at another monitor display. This bug happens even if one display is being used.

I don't know if others are having this bug, or if my setup may be a bit too unique.
Vivaldi version is 2.5.1525.48 (Stable channel) (64-bit), running on Ubuntu 18.04.2 with the KDE Plasma 5 desktop environment (not Kubuntu; this is Ubuntu that came with GNOME with KDE Plasma 5 I installed later).

[Eunoseer]

I can confirm that this is also an issue in Windows Release 2.9.1705.41 (windows 10) with the developer tools window undocked.

I can't quite tell from the original post whether the dropdown menu is still usable or not, but in my case, I am not able to select anything from the dropdown when it displays separately as shown in the original message.

As a workaround, I am able to select items from the dropdown if I dock the developer tools within the browser. However, if I have to frequently change the settings and actively use the developer tools for other tasks, this becomes cumbersome.

Bug report VB-60265 has been created relating to this.