Editing in a watch window

["Fred Young" <fred@nextnewgig.com>]

I'm running Insight version 5.1 under Cygwin.

When I open the Watch window, add a structured local variable, double click
on a field to modify its value and press Enter, I get a dialog box with the
title:
    Error in Expression
and contents:
    No symbol "MAIN__" in current context.

The name in quotes seems to vary, but it's not the name of the local
variable; it seems to be the last name not found in a symbol table search.
For example if I enter the command
    p Foo
in the Console window and then attempt to edit the field value in the Watch
window again, the error message now becomes:
    No symbol "Foo" in current context.

Interestingly, if I add a global int variable to the Watch window then I can
edit the field of the local variable in the Watch window successfully.

I've determined that the following lines in the method changeValue in the
file variables.tcl are responsible for the dialog box:

 if {[catch {$EditEntry value $new} errTxt]} {
     tk_messageBox -icon error -type ok -message $errTxt \
  -title "Error in Expression" -parent [winfo toplevel $itk_interior]

but I don't know how to debug the problem any further.