April 4th, 2016 - Release of SLF4J 1.7.21
Fixed a memory leak due to a race-condition occurring during SLF4J initialization. In that case, some SubstituteLogger instances may continue to accumulate log events until the JVM eventually runs out of memory. This issue was reported in SLF4J-364 by Jeff Flanigan.
LoggerFactory makes sure to release all resources referenced by SubstituteLoggerFactory post-initialization. See also SLF4J-366