Underlined characters in widget titles rendered incorrectly as ampersands in KDE6

[GloriousEggroll]

Operating System Info

Other

Other OS

Fedora 40, Nobara 39

OBS Studio Version

30.1.0-rc1

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/kTk1mXEjWlGxBQTE

OBS Studio Crash Log URL

No response

Expected Behavior

Characters should be underlined instead of showing a prefixed ampersand (&)

Current Behavior

The random ampersands (&) where underlined characters should be in Scenes/Sources etc:

Steps to Reproduce

i was hitting it in Nobara first, so I spun up a vanilla fedora 40 VM and was able to reproduce
it only happens with OBS + KDE 6
furthermore I can do XDG_CURRENT_DESKTOP=gnome and it works around the bug

Download Fedora 39 ISO and create a VM
Update:
sudo dnf update --refresh
Upgrade to Fedora 40:

sudo dnf install dnf-plugin-system-upgrade
sudo dnf system-upgrade download --releasever=40
sudo dnf system-upgrade reboot

Install kde 6:

sudo dnf install @kde-desktop

Log out then log into Plasma.

Install OBS

sudo dnf install obs-studio

Run it and the issue should be reproduced. I've confirmed it does not happen with KDE 5 or in Gnome.

Anything else we should know?

No response

[derrod]

The translation strings for dock titles have no & so I have no clue how they got there...

What does your en-US.ini for the main UI look like?

[GloriousEggroll]

The translation strings for dock titles have no & so I have no clue how they got there...

What does your en-US.ini for the main UI look like?

unmodified, i rebuilt the package from source, same issue.

issue also goes away if i change the default theme from Yami to system. all other themes cause the same thing.
QT_QPA_PLATFORMTHEME=Breeze QT_STYLE_OVERRIDE=Breeze also does not help. Issue still occurs

[derrod]

Strange but probably some Qt or KDE bug, we don't set those anywhere as far as I can tell so no idea where it's getting them from.

[GloriousEggroll]

qt 6.6.2 by itself its fine -- i checked that
on gnome its fine too even with kde 6 installed while logged into gnome
its something with kde
for more info -- another way i also checked this is like so:

install fedora 39
install obs
update fedora 39 all the way
= perfectly fine

install kde on fedora 39 = perfectly fine

enable kde6 copr repo on fedora 39 and update, then log into plasma = problem

then i thought ok maybe is the copr repo -- so i did a wipe and another install of fedora 39
upgraded it to 40
installed kde 6 from fedora;s official repos, log into plasma
= problem

[GloriousEggroll]

After more digging I found if I remove kf6-ki18n it fixes it. (forcefully via rpm -e --nodeps). Obv, not an actual fix but at least a lead on the cause. I'm going to go ahead and open a bug on the KDE side. I'll close this one once confirmed over there.

[GloriousEggroll]

It's a bug in QT. I tracked it down and managed to patch it.
https://bugs.kde.org/show_bug.cgi?id=482657

closing

[RytoEX]

Thanks for following up on the QTBUG.
Linked from the KDE bug: https://bugreports.qt.io/browse/QTBUG-86407