Executing the attached code on wish from ActiveState 8.
4.[11,13] results
on an unresponsive gui when the user does something of 
this:

* click the Dialog's button labeled as "click me!". 
Then click the ok
  button on the messagebox. [Win2KSP4, ActiveState Tcl/
Tk 8.4.11].

* click the dialog's button labeled as "click me!", 
then click the
  Dialog's title bar, the click the Ok button on the
  messagebox. [WinXPSP2, ActiveState Tcl/Tk 8.4.13].

* click the dialog's button labeled as "click me!", the 
click the Ok
  button on the messagebox, click again the "click me!" 
button, click
  again the messagebox Ok button [WinXPSP2, ActiveState 
Tcl/Tk 8.4.13].

The OS/Tcl version combination is just the setup 
available to
me. Nothing beyond that was tested.

Hi,
thank you for reporting, it is reproductible on windows.
Considering the following code on windows tk without BWidget:
---
pack [button .b -text t -command "tk_messageBox"]
focus .b
raise .
grab -global .b
-EOF-
we get a similar deadlock effect.
As a workaround, I suggest to release the grab (or not use global grabs at all) before opening another window.

This is filed as tk bug  2814003

As a workaround, a tk_messageBox routine might be created like
set grabcur [grab]
if {"" ne $grabcur} {
    grab release $grabcur
}
tk_messageBox ...
if {"" ne $grabcur} {
    grab $grabcur
}

Logged In: YES 
user_id=302287

Could only reproduce after a lot of clicking on the Buttons,
not just the few clicks you reported.

As you use Dialog -modal global this is probably a global
grab which is not released.

File Added - 178772: foo.tcl