ConfugrationConverter treats properties different by type

The ConfigurationConverter is behaving differently depending on if I added an int or a string to a configuration object.

Consider the following code:

01 Configuration confInt = new BaseConfiguration();
02 Configuration confString = new BaseConfiguration();
03 confInt.setProperty("port", 80);
04 confString.setProperty("port", "80");
05 assertEquals(80, confInt.getInt("port"));
06 assertEquals(80, confString.getInt("port"));
07
08 Properties propString = ConfigurationConverter.getProperties(confString);
09 assertEquals("80", propString.getProperty("port"));
10
11 Properties propInt = ConfigurationConverter.getProperties(confInt);
12
13 assertEquals("80", propInt.getProperty("port"));

As you can see the code is basically duplicated one set uses an int the other set uses a String. However an exception blows out of line 11.

'port' doesn't map to a List object: 80, a java.lang.Integer
org.apache.commons.configuration.ConversionException: 'port' doesn't map to a List object: 80, a java.lang.Integer
at org.apache.commons.configuration.AbstractConfiguration.getList(AbstractConfiguration.java:1144)
at org.apache.commons.configuration.AbstractConfiguration.getList(AbstractConfiguration.java:1109)
at org.apache.commons.configuration.ConfigurationConverter.getProperties(ConfigurationConverter.java:116)

I interpreted the interface to mean that everything up to and include line 13 would pass.