Steps to reproduce

(1) Create a content type named "A2"
(2) Create another content type named "A1", with an ezobjectrelationlist field, where "A2" is choosen as "Allowed content type"
(3) Save the "A1" Content type
(4) Edit the "A1" content type again
(5) Now we can see that the "Allowed content type" is set to "A1" instead of "A2"

This position is maintained, unless an "A0" (alphabetically prior to "A1") content type is created. Then the selected "Allowed content type" will became the "A0"