It is not possible to turn off the "Status Hold" check box when editing a membership.
To reproduce this edit the membership of a contact and turn on the status hold and save it. If you edit the membership again and turn off the status hold, on saving the status hold bit is not saved. Therefore reopening the membership will still show the "status hold" as being set.
Found this on 1.8 and have verified the same behaviour on the 1.9 alpha sandbox.