Interestignly the following script does not allow to reproduce, what could be the difference with the demo?

<verbatim>
package require Tk
panedwindow .pw -orient horizontal
for {set i 1} {$i <= 2} {incr i} {
    text .pw.t$i -width 15 -height 8
    .pw.t$i insert end "Text widget $i"
}
.pw add .pw.t1 .pw.t2 -stretch always
pack .pw -expand 1 -fill both
</verbatim>