Bug of Tk 9.0b1?

Question

It seems there is a bug of Tk 9.0b1.

In /tk9.0b1/library/demos/menu.tcl, if you remove all "-underline ..." options, any Alt+key leads to an error.

To reproduce it:

1. remove all "-underline ..." of /tk9.0b1/library/demos/menu.tcl

2. then run command: tk9.0b1 /tk9.0b1/library/demos/widget

3. then choose " Menus and cascades (sub-menus) "

4. press any Alt+key (say, Alt+S)

=> the error:

bad index "": must be integer?[+-]integer? or end?[+-]integer?
bad index "": must be integer?[+-]integer? or end?[+-]integer?
    while executing
"string index [$child entrycget $i -label]  [$child entrycget $i -underline]"
    (procedure "MenuFind" line 19)
    invoked from within
"MenuFind [winfo toplevel $w] $char"
    (procedure "tk::TraverseToMenu" line 14)
    invoked from within
"tk::TraverseToMenu .menu o"
    (command bound to event)

The cause is just in the absence of "-underline..." option of menubar items.

If the option is set as "-underline -1" (attempting to have no underlined characters), the bug remains. However, the weird "-underline 999" solves the problem so that you have no underlined menu characters and no bugs of Alt+key sort.

In Tk 8.6 there are no problems with this. Probably, in Tk 9.0, menu.tcl is to blame, with its " >=0 " clauses.

The issue looks strange as the "-underline" option looks mostly out-date, though useful in some cases.