In my understanding, that only keeps the format for .BR files compatible. If you're talking about source code, option 60 has no effect.
There are other things that could make your programs incompatible. For example, if you use a listview or a grid, even with option 60 on, that program will fail in 4.03 because the syntax for Listviews isn't supported in 4.03. Thats just one example.. there are many syntax changes between those versions that are not nearly so obvious. I ran into this problem before once because of a syntax change that I didn't know wasn't supported in 4.03.
Give us a sample of the corrupted Source Code!