Help in axlFormCreate

Hi all!

I have a problem with my form code as below.

here my code 

axlCmdRegister( "testfm" `get_database )
(defun get_database ()
axlSetFindFilter(?enabled '(noall VIAS NAMEFORM) ?onButtons '(noall VIAS))
axlVisibleDesign(nil)
axlVisibleLayer("VIA CLASS" t)
axlClearSelSet()
AllVias_check = axlGetSelSet(axlAddSelectAll())
axlClearSelSet()
test_frm()
);end defun

form = nil
(defun test_frm ()
Out_File_Form = outfile("./test_frm.form" "w")
.........
close(Out_File_Form)
form = axlFormCreate((gensym) "test_frm.form" nil '_form_Action t)
axlFormAutoResize(form)
axlFormDisplay(form)
);end defun form main

(defun _form_Action (form)
case(form->curField
("start"
printf("test %L\n", AllVias_check)
);end case start
...........
);end case all
);end defun

The problem occur when I click on Start button, variable "AllVias_check" return dbid: removed. But if I change  '_form_Action t  into '_form_Action nil  variable "AllVias_check" return list of dbib.  Please help me to understand it.