ToolBar's TB_FLAT flag has no effect on GTK?

http://wxpython.org/Phoenix/docs/html/ToolBar.html#toolbar says TB_FLAT “gives the toolbar a flat look (Windows and GTK only)”, however the script below renders 3 identical toolbars on my system.
By the way, trying to print the value of TB_DEFAULT_STYLEraises AttributeError.
My intention would be to create a ToolBar without any kind of borders, i.e. absolutely flat: any way to do it?

My system:
Arch Linux x86_64
GTK+ 2.24.22
wxGTK 3.0.0
wxPython 3.0.0.0

···

#######################################
import wx

class ToolBar(wx.ToolBar):
def init(self, parent, style=0):
super(ToolBar, self).init(parent, style=style)
self.AddLabelTool(0, “”, wx.ArtProvider.GetBitmap(
wx.ART_QUESTION, wx.ART_TOOLBAR))
self.Realize()
print(‘Style’, self.GetWindowStyleFlag())

app = wx.App()
frame = wx.Frame(None)

print(‘TB_HORIZONTAL’, wx.TB_HORIZONTAL) # 4
print(‘TB_FLAT’, wx.TB_FLAT) # 32
print(‘BORDER_NONE’, wx.BORDER_NONE) # 2097152

box = wx.BoxSizer(wx.VERTICAL)
frame.SetSizer(box)

for toolbar in (ToolBar(frame), # 4
ToolBar(frame, style=wx.TB_FLAT), # 36
ToolBar(frame, # 2097188
style=wx.BORDER_NONE | wx.TB_FLAT)):
box.Add(toolbar, flag=wx.EXPAND | wx.ALL, border=20)

frame.Centre()
frame.Show()
app.MainLoop()
#######################################

Thank you