I cannot replicate the behavior on your site, which I presume is EF 5.1.6
Also, I am encountering an error when I attempt to import a simple form with two labels and two select lists where this behavor exists.
If this is an issue in EF 5.1.4 and not in 5.1.6 then I need a fix for 5.1.4.
Please demonstrate for yourselves by doing the following:
create a template in EF 5.1.4 with
1) a select list with two or three selections like
S|Select
B|Blue
G|Green
2) another select list with conditional visibility based on the value of the first select list equal "B"
test and you see it works as required.
Now put "mandatory" on the second select list and see that it no longer obeys visibility rules.