We run multiple apps in the same instance of Mule (ESB product), all in the same JVM. We use a context selector to setup each app with its own logging context at startup. This has worked fine for quite some time, we haven't upgraded/changed any slf4j or logback dependencies, and it suddenly stopped working. What's happening now is that we're getting parts of our logging ending up in other context's log files. For example, we'll get a WARN message in the appropriate log file, but then a stack trace for that app will get logged to a different context's log file. It ends up in the same log file every time we restart, so it seems to be repeatable. Even if we remove all but two apps from the JVM, we can show that even with just those two apps they log to each other's log files. Any ideas out there for me to try?