Pressing Alt+F1 with mouse cursor over the Applcations leads to focus move to Applications, the menus are unusable as result

[Norbert]

Steps to reproduce:
1. Have Ubuntu MATE 20.04 LTS installed
2. Login to session, choose Traditional desktop layout in MATE Tweak
3. Move move cursor over Applications menu
4. Press <Alt>+<F1> to open Applications menu
5. Press <RightArrow> or <LeftArrow>

Expected results:
* focus moves with <RightArrow> or <LeftArrow> to corresponding one of the menu items - Applications, Places, System

Actual results:
* focus is stuck on Applications menu, about which mouse cursor is located (see screencast)

ProblemType: Bug
DistroRelease: Ubuntu Kylin 20.04
Package: mate-panel 1.24.0-2 [origin: Ubuntu]
ProcVersionSignature: Ubuntu 5.4.0-29.33-lowlatency 5.4.30
Uname: Linux 5.4.0-29-lowlatency x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: MATE
Date: Sun May 10 18:57:48 2020
InstallationDate: Installed on 2020-04-22 (17 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Release amd64 (20200422)
SourcePackage: mate-panel
UpgradeStatus: No upgrade log present (probably fresh install)

[Norbert (nrbrtx)]

Caused by some mess with customizations from other flavors.
The normally installed Ubuntu MATE is not affected.