Closed design and corrupted compiled code

So my current company supply packaged Lotus Notes applications, which get implemented with hidden designs. I'd made some design changes and applied them to the client's application, obviously having done the usual UAT testing and so on. Imagine my surprise when the production application started playing up.

With the customer's help, I was able to reproduce the effect and determine that the issue occurred only when applying the design with the "Hide formula and LotusScript" option checked, i.e. closed design. That got me to thinking about the nature of templates.

Templates contain both raw code and compiled code. When you replace the design so that it's closed, only the compiled code is used. It seems the compiled code was corrupted, which is why it worked with the open design but not the closed one.

That lead me to the solution. I had to recompile all the LotusScript to make sure the template contained the correct compiled code. That sorted the problem straight away. So hopefully this helps someone else.