Corruption wouldn't be the first thing I'd look for in this case. More likely, you have an auto-enter calculation, a lookup, or a crossup in your script someplace that's inserting the information from a related record. Check there first.
I agree with Mike.
While it ultimately may be some form of corruption I would not jump to that conclusion based on the description you provided. I'd explore other avenues for sure first and save file corruption as a last resort.
To piggyback on Mike's suggestions - I'd turn on the Script Debugger and walk through the script attached to the button and make sure it is doing what you think it should be doing. That would be a good first step in tracking down the behavior you are seeing.
FileMaker Pro Advanced required for ScriptDebugger, of course. No developer (in-house or in-dependent) should be without it.
Saves my bacon many a time.
Please provide more detail e.g. is address a lookup ? or a fixed "set field" step ?
if it's a Related value, and your Field Index is scrambled, it might "find" the wrong result
Wow! thanks for the answers guys/gals. I did figure it out. At the beginning of setting up the solution, i had imported some dummy data into an address table. Forgetting to delete the data, it appears that when entering a new record the matching id in the address table was carried over. I deleted the data and all is good.