Checkboxes overlapping in JIRA 6.2

I imported my data from JIRA 6.1.5 where I had defined custom checkbox.
First time it shows up normally. I had both check boxes selected.
1. I deselected "two" from issue screen, everything still is OK as in Screenshot1.png
2. When I want to edit it again, I see them overlapping with "two" in front of "one" without any possibility to check or un-check "one". I can still check "two". See Screenshot2.png

I am not sure if it helps, but I attached Screenshot3.png that shows configuration of this checkbox field.

Kind regards,
Lauma