Using "libs" and "lib" directories?

I use the directory "libs" for a native libs, and "lib" for jars. Ant compilation works fine, if to override the property "jar.libs.dir=lib" in local.properties file. looks good. But a jars from "lib" directory was not included into APK file.

You can see base build.xml (android_sdk/tools/ant/build.xml)

            <classpath>
                 <fileset dir="${extensible.libs.classpath}" includes="*.jar" />
             </classpath>
 

where extensible.libs.classpath - is jar.libs.dir.

How to fix it? I can't to use only one "libs" dir.

I saw the log file (classes.dex.d), my jars are not included. but if I use "jar.libs.dir=lib" AND move the jars into "libs" - works fine! I don't understand this regularity

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