Hi, I am having the same problem:

28-Sep-2016 18:09:53.883 SEVERE [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoader.checkThreadLocalMapForLeaks The web application [] created a ThreadLocal with key of type [ch.qos.logback.core.UnsynchronizedAppenderBase$1] (value [ch.qos.logback.core.UnsynchronizedAppenderBase$1@75935153]) and a value of type [java.lang.Boolean] (value [false]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
28-Sep-2016 18:09:53.884 SEVERE [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoader.checkThreadLocalMapForLeaks The web application [] created a ThreadLocal with key of type [ch.qos.logback.core.UnsynchronizedAppenderBase$1] (value [ch.qos.logback.core.UnsynchronizedAppenderBase$1@1e12761]) and a value of type [java.lang.Boolean] (value [false]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
28-Sep-2016 18:09:53.884 SEVERE [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoader.checkThreadLocalMapForLeaks The web application [] created a ThreadLocal with key of type [ch.qos.logback.core.UnsynchronizedAppenderBase$1] (value [ch.qos.logback.core.UnsynchronizedAppenderBase$1@f0dcfd2]) and a value of type [java.lang.Boolean] (value [false]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
28-Sep-2016 18:09:53.884 SEVERE [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoader.checkThreadLocalMapForLeaks The web application [] created a ThreadLocal with key of type [ch.qos.logback.core.UnsynchronizedAppenderBase$1] (value [ch.qos.logback.core.UnsynchronizedAppenderBase$1@69b9bdfd]) and a value of type [java.lang.Boolean] (value [false]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.

I am using:
ch.qos.logback:logback-classic:jar:1.1.7 , ch.qos.logback:logback-core:jar:1.1.7, tomcat 8.0.11

This ticket says the fix was in version 0.9.26 - so this actually shouldn't happen?