Strange behavior with some keyboard shortcuts

[skyper]

What steps will reproduce the problem?

1. Ctrl+Shift+E or Ctrl+Shift+U

What is the expected result?

The action assigned with the shortcut otherwise nothing

What happens instead?

A text input field appears below the status line with the respective letter and possibility to enter more.
The shortcut is not usable within JOSM but utilsplugin2's "Select all connected ways" has Ctrl+Shift+E ad default.

Please provide any additional information below. Attach a screenshot if possible.

I noticed this first with the non-working utilsplugin2 action but it is visible without any plugin and complete new preferences
So far, I tried java 11 and 17 plus have created a new user with i3 as desktop environment (instead of Gnome) but without any differences.

All other shortcuts even with Ctrl+Shift seem to work.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-08-31 23:17:15 +0200 (Tue, 31 Aug 2021)
Revision:18187
Build-Date:2021-09-01 01:31:03
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (18187 en) Linux Debian GNU/Linux 11 (bullseye)
Java version: 11.0.12+7-post-Debian-2, Debian, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.metal.MetalLookAndFeel
Desktop environment: i3
Java package: openjdk-11-jre:amd64-11.0.12+7-2
libcommons-compress-java: libcommons-compress-java:all-1.20-1
libcommons-logging-java: libcommons-logging-java:all-1.2-2
fonts-noto: fonts-noto:all-20201225-1
VM arguments: [--module-path=/usr/share/openjfx/lib, --add-modules=java.scripting,java.sql,javafx.controls,javafx.media,javafx.swing,javafx.web, -Djosm.restart=true, -Djosm.dir.name=JOSM-la<user.name>, -Djava.net.useSystemProxies=true]

[skyper]

Oh no, it is the ibus-emoji shortcut, see ​https://unix.stackexchange.com/questions/569366/how-to-disable-gnome-ctrl-shift-e-emoji-popup