API edit control losing focus on arrow keys

This thing keeps me in "what the..." category: whenever I push an arrow key in an edit control that I have created using API, the focus moves to any other control that is available. However, none of the tutorials, guides etc. have a mention about this feature. What causes this and how can I get the "normal" behavior for the arrow keys? Page up, down, home and end are working, but arrow keys not.

Also, I haven't seen a style flag that would affect this behavior.

I couldn't duplicate the problem.
Are you sure something isn't wrong in WndProc ? Have you tried in a fresh project ?
Can you post the code ?

For more details, I've wrapped the control in an usercontrol; and I can't make it much more "fresh" than it is.

VB Code:

' init styles
    lngStyle = WS_CHILD Or WS_VISIBLE Or ES_NOHIDESEL
    If m_MultiLine Then
        Select Case m_ScrollBars
            Case vbSBNone
                lngStyle = lngStyle Or ES_MULTILINE Or ES_AUTOVSCROLL Or ES_AUTOHSCROLL
            Case vbHorizontal
                lngStyle = lngStyle Or ES_MULTILINE Or ES_AUTOHSCROLL Or WS_HSCROLL
            Case vbVertical
                lngStyle = lngStyle Or ES_MULTILINE Or ES_AUTOVSCROLL Or WS_VSCROLL
            Case vbBoth
                lngStyle = lngStyle Or ES_MULTILINE Or ES_AUTOHSCROLL Or WS_HSCROLL Or WS_VSCROLL
        End Select
    Else
        lngStyle = lngStyle Or ES_AUTOHSCROLL
    End If
    
    ' create new textbox
    m_hWnd = CreateWindowExW(0&, StrPtr("Edit"), StrPtr(m_Text), _
        lngStyle, _
        m_BorderStyle, m_BorderStyle, m_RC.Right - m_BorderStyle * 2, m_RC.bottom - m_BorderStyle * 2, _
        UserControl.hWnd, 0&, App.hInstance, 0&)

This is the part of the code that creates the edit control; before that only properties are read, then this code is next to be called. The only other extra I can think of is that the host usercontrol redirects the focus automatically to the edit control. Nothing else should have effect on the default behaviour of the control.