bug#3192: 23.0.92; disabling tooltip-mode inhibits showing Customize error msgs

emacs -Q
 
(defcustom foo nil
  "..."
  :type '(alist :key-type (symbol) :value-type (function)))
 
M-x customize-option foo
 
Edit the Function field to nil (which is an invalid value).
Click the State button and choose Set for Current Session.
 
You see the message "Invalid function: nil" in the echo area.
 
M-x tooltip-mode (to turn it off)
 
Click the State button again and choose Set...
 
No message is displayed. The message is logged in *Messages*, but the
user sees nothing to indicate what, if anything, happened.
 
Disabling tooltip-mode should mean only that mouseover :help text gets
displayed in the echo area. It should not mean that if the mouse is
over something (such as the State button) that has :help text defined
then normal messages (including error messages) are inhibited.
 
Also, clicking a button such as State, and choosing one of its menu
items, should remove any mouseover :help text from the echo area -
regardless of whether the menu item's invocation results in a message.
 

In GNU Emacs 23.0.92.1 (i386-mingw-nt5.1.2600)
 of 2009-03-30 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'