Undefined Symbols for QT Plugins on Closing App

[Parker Newman]

I have a application that using many plugins with a custom interface. They work great however sometime when I close the GUI using the X, I get the following error:

<executable name >symbol lookup error: <the plugin path>/libDisplayTest.so: undefined symbol: _ZN19TestPluginInterfaceD2Ev
<executeable name> exited with code 127

TestPluginInterface is my plugin interface.

It seems like my plugins are not being unloaded automatically on the exit of the program?

Here is a snippit of how I load a plugin (error checking removed).

TestPluginInterface* TestManager::loadPlugin(QString pluginName)
{
    QPluginLoader pluginLoader(pluginPath,this);
    pluginObject = pluginLoader.instance();
    testPlugin = qobject_cast<TestPluginInterface*>(pluginObject);
    return(testPlugin);
}

Any ideas? I do not explicitly delete the plugin pointer anywhere.

[Parker Newman]

I figure this out.
I had to change the destructor od my interface from

virtual ~TestPluginInterface() = 0;

to:

virtual ~TestPluginInterface() = default;