Basically, using a BufferedInputStream to read 0 bytes over a socket blocks with 1.5 whereas the same operation does not block using 1.4. The netscape ldapjdk relies on the behaviour seen in 1.4. Actually, I can confirm that the problem does not occur for J2SE 1.5.0-beta-b32c and does occur for J2SE build 1.5.0-beta2-b45, so somewhere in between the behaviour changed.