That was strange as Google is veryfing packages just after upload - if the package was built in release mode etc. so I would expect Google to show at least some warning. But it acted like everything was in the best order.
The problem was I was using JDK 7! Default digest algorithm for Java 7 is SHA-256 instead of SHA-1 used in JDK 6. As Android APKs have to use SHA-1 to compute checksums for included files, default JDK 7 settings made resulting APK unusable. I think Google should check this in it's post-upload process.
To resolve this issue add the following lines to build.xml forcing the digest algorithm to be SHA-1.
<presetdef name="signjar"> <signjar digestalg="SHA1" sigalg="MD5withRSA"> </signjar> </presetdef>