Hi Johann,
Been trying your patch and it works well. Certainly doesn't seem to break the routing. However, it doesn't always merge ways that, as far as I can tell, should be merged. I have studied your code so I know how you're doing the matching. One thought, would rounding the coords before merging help? If it isn't that, something else must be not quite right.
Yes, I have been trying for myself the last hour and detected too, that some lines should be connected, but aren't. I had not found out the error for now. But I've seen line endings not matching exactly. Don't now if it had to do something with the rounding. I don't think, that rounding before merging will help, but will have a look at it. I need to prepare some test cases. Regards, Johann