wxpython collapsible panes inconsistent sizing response

Okay so, something's odd and I can't figure it out. Suppose I've got some categories, each with some items, all fitted into a dictionary.

import wx
nyoom = {}
nyoom['spiders'] = ['Yellow Sac', 'Orbweaver', 'Garden']
nyoom['cats']= ['Bombay','Angora']
nyoom['cambrian'] = ['Wiwaxia','Hallucigenia','Pikaia','Alomancaris']

Then I want to display each category as a button which collapses or displays all of that category's contents as buttons as well.

class SeqFrame(wx.Frame):
    def __init__(self):
        wx.Frame.__init__( self, None, wx.ID_ANY, "GUI Woes", size=(400,400))
        self.panel = wx.Panel(self, wx.ID_ANY)
        sizer = wx.FlexGridSizer(cols=2, hgap=5, vgap=5) #sizer for the window
        numActsTxtBox = wx.TextCtrl( self.panel, -1, "1", size=(40, -1))
        numActsTxtTxt = wx.CheckBox( self.panel, -1, "Number of Times")
        sizer.Add( numActsTxtTxt, 0, wx.ALL )
        sizer.Add( numActsTxtBox, 0, wx.ALL )
        for categories in nyoom.keys():
            self.categPanes=[]
            self.categPanes.append(wx.CollapsiblePane(self.panel, -1, label=categories))
            self.buildPanes(self.categPanes[-1], sizer)
            thisPanel = self.categPanes[-1].GetPane()
            panelSizer = wx.BoxSizer( wx.VERTICAL ) #sizer for the panel contents
            sortedCategory = nyoom[categories]
            sortedCategory.sort()
            for i in range(0,len(nyoom[categories])): 
                thisSeq = wx.Button( thisPanel, label=sortedCategory[i], name=sortedCategory[i])
                panelSizer.Add( thisSeq, 0, wx.GROW | wx.ALL ,0 )
        thisPanel.SetSizer(panelSizer)
        panelSizer.SetSizeHints(thisPanel)
        self.panel.SetSizerAndFit(sizer)
        self.Fit()
    def buildPanes(self, categPane, sizer):
        categPane.Bind(wx.EVT_COLLAPSIBLEPANE_CHANGED, self.OnPaneChanged)
        sizer.Add(categPane, 0, wx.GROW | wx.ALL, 0)
    def OnPaneChanged(self, evt):
        self.panel.GetSizer().Layout()
        self.panel.Fit()
        self.Fit()

if __name__ == '__main__': 
    app = wx.App()
    frame = SeqFrame()
    frame.Show(True)
    app.MainLoop() 

(That's my entire sample app.) I can't figure out why, but everything works fine for the last category in the dictionary: But the previous categories can only display one button/item.

thisPanel is being set inside your loop, but you're calling SetSizer after the loop, so only the last thisPanel gets a sizer. Move the call to SetSizer inside the loop.