@PreDestroy annotated method is not called

When annotating the DomainService "SimpleObjects" with
...
@PostConstruct
@Programmatic
public void init()

{ System.out.println(">>> @PostConstruct init called <<<"); }

@PreDestroy
@Programmatic
public void shutdown()

{ System.out.println(">>> @PreDestroy shutdown called <<<"); }

...

only the @PostConstruct method will be called out of the box.
Unfortunately, the annotated @PreDestroy method not.

How to reproduce:
1) Checkout, build and check that Simpleapp 1.7.0 or 1.8.0-Snapshot is running.
2) Introduce the mentioned @PostConstruct and @PreDestroy methods
an go sure, that a message will be logged when message is called.
3) build and deploy simpleapp-webapp.war to Tomcat v7.x or Tomcat v8.x
4) See log / use breakpoints to see that @PostConstruct method will be successfully called.

15:40:18,311 [Schema Thread-2 DEBUG] Schema Transaction closing with connection "org.datanucleus.store.rdbms.datasource.dbcp.PoolingDataSource$PoolGuardConnectionWrapper@74ce8acd"
>>> @PostConstruct init called <<<
15:40:24,504 [Reflections Thread-2 INFO ] Reflections took 3181 ms to scan 125 urls, producing 9629 keys and 59986 values

5) Stop simpleapp-webapp or redeploy it or even stop tomcat
6) See log / breakpoints and realize that no @PreDestroy method was called.

Negativ side effect is, that every associated connection to JMS / Elastic Search, ... in @PostConstruct cannot be disconnected easily and cleanly.

As a workaround I have tried to activate the section in web.xml:

<!--
THE FOLLOWING CONFIGURATION IS NOT REQUIRED IF THE WICKET VIEWER IS IN USE.
IF THE WICKET VIEWER CONFIGURATION IS REMOVED, THEN UNCOMMENT
-->

<listener>
<listener-class>org.apache.isis.core.webapp.IsisWebAppBootstrapper</listener-class>
</listener>

<context-param>
<param-name>deploymentType</param-name>
<param-value>SERVER_EXPLORATION</param-value>
</context-param>

<context-param>
<param-name>isis.viewers</param-name>
<param-value>restfulobjects</param-value>
</context-param>

even this is not my scenario. Doing this the annotated methods gets called, but I hit the IsisWicketApplication Error:
Failed to initialize
com.google.inject.ProvisionException: Guice provision errors:

1) Error in custom provider, org.apache.isis.core.commons.exceptions.IsisException: Isis Context already set up and cannot be replaced
at org.apache.isis.core.runtime.runner.IsisInjectModule.provideIsisSystem(IsisInjectModule.java:132)
at org.apache.isis.core.runtime.runner.IsisInjectModule.provideIsisSystem(IsisInjectModule.java:132)
while locating org.apache.isis.core.runtime.system.IsisSystem
for field at org.apache.isis.viewer.wicket.viewer.IsisWicketApplication.system(IsisWicketApplication.java:140)
while locating webapp.SimpleApplication

The cool thing is, that this time both annotated method are called:

16:16:37,713 [Schema Thread-2 DEBUG] Schema Transaction closing with connection "org.datanucleus.store.rdbms.datasource.dbcp.PoolingDataSource$PoolGuardConnectionWrapper@2339e31f"
>>> @PostConstruct init called <<<
16:16:45,196 [Reflections Thread-2 INFO ] Reflections took 3259 ms to scan 125 urls, producing 9629 keys and 59986 values
...
INFORMATION: Cleaning up Shiro Environment
>>> @PreDestroy shutdown called <<<

16:16:53,198 [IsisContext main INFO ] closing all instances
16:16:53,198 [IsisWebAppBootstrapper main INFO ] server shut down

Please fix that issue or assist me in creating a workaround.
Thanks,
Peter