Just wanted to jump in and say that I am also experiencing this issue with logback-classic:1.2.3. I am able to reliably reproduce this issue with an application we are working on. I have attached a debug log which demonstrates the issue. You can see that the application starts logging a larger and larger amount of log messages per unit of time until eventually the application hangs (stop responding to all input) indefinitely: debug-LOGBACK-1406.log^.