agw AuiToolBar raises AssertionError in ShowDropDown (Ubuntu)

Ubuntu 18.10:

Python 3.7.1 (default, Oct 22 2018, 11:21:55) [GCC 8.2.0]

wxPython 4.0.3 gtk3 (phoenix) wxWidgets 3.0.5

Windows 10 (1803):

Python 3.7.1 (v3.7.1:260ec2c36a, Oct 20 2018, 14:57:15) [MSC v.1915 64 bit (AMD64)]
wxPython 4.0.3 msw (phoenix) wxWidgets 3.0.5

The attached script shows a toolbar (agw) with a tool that has a drop down menu. On Windows the drop down menu is shown, but on Ubuntu i get this exception:

Traceback (most recent call last):
File “/scratches/scratch_1.py”, line 95, in on_new_sheet_dropdown
art_provider.ShowDropDown(tb_service, menu_popup)
File “/venv37/lib/python3.7/site-packages/wx/lib/agw/aui/auibar.py”, line 1438, in ShowDropDown
m.SetBitmap(item.GetBitmap())
wx._core.wxAssertionError: C++ assertion “Assert failure” failed at /home/vagrant/wxPython-4.0.3/ext/wxWidgets/src/gtk/menu.cpp(729) in SetBitmap(): only normal menu items can have bitmaps

``

Are drop down menus with icons not possible on Ubuntu or is this a bug (in wxWidgets)?

scratch_1.py (2.81 KB)