Icons on buttons missing

Icons are missing on some buttons of both "Find" and "Search in Files" panes.

The attached screenshot show buttons with missing icons. (I encircled the buttons without icons with a red curve in the shots.)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: kate 4:17.12.3-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-33.36-generic 4.15.18
Uname: Linux 4.15.0-33-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sat Sep 8 19:19:17 2018
InstallationDate: Installed on 2018-06-23 (76 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IL
 SHELL=/bin/bash
SourcePackage: kate
UpgradeStatus: No upgrade log present (probably fresh install)