Yes, I am also a bit unhappy that the move to Karaf causes quite some new problems that previously didn’t exist. But still I think that its benefits weigh more than the problems, so I decided to better do the move now than later.
Regarding the concrete problem in the weather binding: I have no idea what this means, this probably need some code analysis.
At a first glance, I guess this line is the problem: openhab1-addons/bundles/binding/org.openhab.binding.weather/src/main/java/org/openhab/binding/weather/internal/parser/CommonIdHandler.java at main · openhab/openhab1-addons · GitHub
Resources should be loaded through the bundle context, not via the classpath - I would assume that this fixes the issue.