For some reason I couldn't reproduce this issue. I tested with 3 and 4 regions but I was always able to add the event handler. Can you send us a sample app perhaps?
Like you, I could not reproduce the problem on a new project. Since I could not share the project without my customer's approval, I prepared a copy of the page with the problem and added a few lines of patches to fix the errors.
The project I shared does not contain any meaningful code in itself ( Please forgive me for this code). But this code can reproduce the issue. I kept the structure and
I could not catch the real position of the problem in my first post. I thought the problem was related to the number of #regions because the problem was removed after I put the remark signs on two region headers. But if only the second region (Custom properties/variables) gets the remark signs the problem disappears.
The following picture shows a problemless configuration.
When you remove the remark signs you can not add a new event.
There is a trailing " which confuses our current implementation. You can delete the " and things will work again. We will try to support this case though - it is valid C# which our tokenizer should handle.