Difficulties with change of time signature

[Die5Willes]

Hi there!
The piano sonata op.78 by L. v. Beethoven starts with \time 2/4 and right in 
the middle of bar 4 there is a double bar line: \bar "||" and a change of time 
signature: \time 4/4 for the rest of the entire movement. Here's my .ly-Code 
showing bars 4-6:

\score {
        \notes\context PianoStaff < \context Staff = one { \time 2/4 \clef 
violin \key fis \major 
%bar4
        < \context Voice = VA { \stemUp b'32 ais' dis'' cis'' cis''8-\fermata} 
\context Voice = VB { \stemDown fis'8}   > \bar "||" \time 4/4  ais'8. b'16 
\bar "|"
%bar5   
        cis''4 < \context Voice = VA { \stemUp fis'4 eis'  fis'} \context Voice 
= VB { \stemDown cis'4 cis' cis'}>
%bar6
        <b2. cis'2. eis'2. b'2.> <gis4 cis' gis'>

}
        
        \context Staff = two { \clef bass \key fis \major

%bar4
        <fis,,4 fis,4-\fermata> \bar "||"  r4 \bar "|" 
%bar5
        fis,8 fis (ais fis b fis ais) fis
%bar6
        gis8 cis gis cis gis cis eis cis}>
}

The .ps file coming out of this prints the double bar line in bar 4 and makes 
the changing of time signature; everything's fine so far. But it doesn't seem 
to take notice of the new 4/4 time. The first bar line after the "b'16." is ok 
but the next one is wrong: it still seems to be a 2/4, see?
What is wrong in that code?
Could somebody please help me??
Nice Greetings
    Brahms