Setting focus to True on TextInput crashes app in Windows

[KaitainJ]

This is with

[INFO   ] [Kivy        ] v1.10.1
[INFO   ] [Python      ] v2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 20:19:30) [MS
C v.1500 32 bit (Intel)]

This code works perfectly on Linux but trashes the app with a fatal freeze on Windows.

def createTextInputPrompts( promptAndDefaultPairs ):

    assert thisIsMainThread()
    boxLayout = GridLayout(cols=1)


    primaryInput = None


    for [prompt, default] in promptAndDefaultPairs:
        label = Label(text=prompt)
        textinput = TextInput(text=default, multiline=False)
        if not primaryInput:
            primaryInput = textinput
        textinput.write_tab = False
        textinput.bind(focus=textInputGotFocus)
        boxLayout.add_widget( label )
        boxLayout.add_widget( textinput )
    return [boxLayout, primaryInput]

Client code:

def tryToSetInitialFocus( self ):
        if self.m_PrimaryInput:
            print( "Will attempt on " + str( self.m_PrimaryInput ) )
            self.m_PrimaryInput.focus = True
            print( "Set focus ")
            self.m_PrimaryInput = None

Output:

[INFO   ] [Base        ] Start application main loop
[INFO   ] [GL          ] NPOT texture support is available
Will attempt on <kivy.uix.textinput.TextInput object at 0x0401EC38>

(Dies horribly at this point, requiring manual shutdown of frozen app.)

The app also waits for a few hundred ms after widget creation before calling tryToSetInitialFocus(). I tried extending this on Windows, but it made no difference. As I say, it all works beautifully in Linux. Also makes no difference if I remove the focus binding. 

If I remove the call to tryToSetInitialFocus(), everything in the rest of the app works fine in Windows. It's the one piece of functionality I can't get working on it, requiring manual mouse click focusing on every new text input dialog. (It's happy for me to tab around subsequently.)