Ibus hangs when I press Supr, Backspace, CTRL+V on text edit, MATE wxWidgets GTK3, and GUI window rendering artefacts

Description

I have a weird issue on EEschema, not sure since when, probably a couple of weeks, in case it is related with some library update. But maybe it is older and I did not notice it before just by chance as I had not been using KiCad for a couple of months. When I open a symbol, and want to edit one of the values or datasheets, for example pressing on Supr, Backspace, CTRL+X, CTRL+V, etc. Eeschema hangs for several seconds. It does not hang when I type letters from the keyboard. Only if I delete already existing ones. Or I press CTRL+V on empty fields. When hanging, I see my CPUs using 4 cores suddenly and my ventilator starts to run.

Steps to reproduce

1. Open a symbol in a schematic by pressing E
2. Change one character a field by pressing backspace once
3. Becomes unresponsive. Wait 10 to 20 seconds until it accepts the deletion.
4. Add more characters, this has no delay.

KiCad Version

Application: Eeschema
Version: 5.1.5-52549c5~86~ubuntu18.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.58.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-99-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.5.0 with C++ ABI 1011

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=ON
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON