Looking at the source code of your Browser you will find that output of 4.2 will always have a precedent empty line, while 4.1 had not.
Sometimes the issue is that white space in cf sucks. Ito solve everything I would have to code everything in one line.
Looks like the issue got way better in ColdBox 4. Backporting my sample app to Coldbox 3.8.1 had 130 extra lines of whitespace! The script conversion probably got rid of a bunch of the tag functions that were leaking whitespace. We just need to track down the function still left in ColdBox 4 that doesn't have output=false.
I have located the issue. It's in the InterceptorService because output is set to true in the processState method. I have converted this method to script (and output is still set to true!) and the extra whitespace is now gone. Pull request coming soon.