Odd behavior in Python/Tkinter?

[Lie]

> But an expression (e.g. string) is NOT a variable. It's fine if the
> value mirrored when I set the textvariable conf to the same variable,
> but in this case I'm setting them to the same expression (e.g. string).

On the other hand, the oddness multiplied since the value replication
doesn't happen if I set the textvariable to a variable. So, why is it?
A checkbox/optionbox value replication works if they're set to a
variable (I don't know if they're set to an expression) but Entry's
value replication works only if they're set to expression not variable.