wx.html2.WebView.RegisterHandler broken in 4.2.1 (regression from 4.1.1)

[mmmmichael]

Operating system: Windows 11.
wxPython version & source: 4.2.1 via pip.
Python version & source: Official Python 3.9.1 installer for Windows.

Description of the problem:

1. Run https://github.com/wxWidgets/Phoenix/blob/wxPython-4.2.1/samples/html2/webview_sample.py.
2. Type custom:abc into the "Location:" field and press Enter.
3. The webview does not show the text "Custom Handler Example", see first screenshot.
4. For comparison: It is shown correctly in 4.2.1, see second screenshot.

I looked a little bit into the source code, but didn't see any significant change to the IE implementation of the WebView, except that the IE version was increased in 130959f.