I've had an odd one happen. I have a front end and a back end in a system. When updating the system, I create a copy of both then work on the front end. (I always back up before copying obviously!). When I test, the back end gets extra data obviously.
I've noticed an anomaly now. This morning I added a few scripts to the front end, using fields which have always been there. I tested and all worked fine. As the back end now had extra data as a result of the test, I dropped the original back end into the folder with the modified front end. The scripts for the front end are now wrong - looking for the wrong field. All that I did was drop the copy of the good back end into the folder with the modified front end. The process:
Delete back end with extra data from working folder
Copy original back end into working folder
Anyone seen this before?