Here is a test Wapp script I am using:

<blockquote><verbatim>
source ./wapp.tcl
proc wapp-default {} {
  wapp-trim {
    <p>Visit the <a href='%html([wapp-param
    page for a slow-to-load case.</p>
  }
}
proc wapp-page-slow {} {
  set x [expr {abs(int(rand()*100000))}]
  for {set i 0} {$i<20000000} {incr i} {
    set x [expr {$x+1}]
  }
  wapp-trim {
    <h1>Slow page</h1>
    <p>x = %html($x)</p>
  }
}
wapp-start $argv


I run this as "tclsh slow.tcl --server 8080" and then look at the /slow page
in a webbrowser.  Then I start hammering the refresh button.  Everything works
fine for me.  No errors.  (Tcl 8.7, Firefox, Ubuntu)

Do you have another test case that will better demonstrate the problem?