Hat sich erledigt. Ich hab mir selbst ein Bein gestellt und in der falschen Reihenfolge gesplittet...
# Vorher
$self->{'SPLIT1'}->SplitHorizontally($self->{'SPLIT2'}, $self->{'LOG'}, $CONF{'sash1'});
$self->{'SPLIT2'}->SplitVertically($self->{'NOTEBOOK'}, $self->{'SPLIT3'}, $CONF->{'sash2'});
$self->{'SPLIT3'}->SplitHorizontally($self->{'LIST'}, $self->{'PAN'}, $CONF->{'sash3'});
# Jetzt
$self->{'SPLIT3'}->SplitHorizontally($self->{'LIST'}, $self->{'PAN'}, $CONF->{'sash3'});
$self->{'SPLIT2'}->SplitVertically($self->{'NOTEBOOK'}, $self->{'SPLIT3'}, $CONF->{'sash2'});
$self->{'SPLIT1'}->SplitHorizontally($self->{'SPLIT2'}, $self->{'LOG'}, $CONF{'sash1'});
Doh! Da muss man erstmal drauf kommen...