Please see 6198196. The submitter provided this additional information:

"1. We have seen the message on the Windows platforms (at least Windows XP
and Windows 2000 Professional), but not on linux.
2. We see the message from both javac and apt. In javac it is an error,
while in apt the message is printed, but it doesn't appear to be included
in the count of errors or warnings."

This would indicate that apt sometimes ignores javac errors. Also, apt
should ensure that it is not exposed to the same problem due to copy and
paste. Se suggested fix of 6198196.