Until someone with more knowledge of bugs (*cough* Phil) comes by to reply, I'm going to wager a guess that the records aren't locked down as tightly as you might think (it's hard to believe such a glaring security hole would be present across so many versions).
Anyway, could you please describe in detail how your archived records are "completely secured?" If it doesn't involve a record-level permissions check in Manage Security (and throw in some conditional field validation too), they aren't completely secured. (Note: Even if you do everything right in Manage Security, a stray drag by a full-access user such as yourself could still bypass your security settings, insofar as you're literally full-access. That's why using validation as a backup could be helpful. Or, you know, just stay away from dangerous layouts when you're logged in as full-access.)
I too would like to know what you mean by "completely secured". If I use Field Behavior to block access to a field while in browse mode, I can't drag or drop any data into the field. And if Manage | security settings prohibit access to the field, I can't modify it either.
I suspect that you are trying to use script triggers to block modification of the field. Drag and Drop will evade tripping script triggers such as OnObjectEnter and OnObjectSave but will trip OnObjectModify Script triggers aren't the best option for controlling access and this is why. Script triggers are good for preventing mistakes but not for providing true security.
You might want to read this section in the FileMaker help system:
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a detailed description of how to set this up.