Piping from stdin is broken

Version: master (ace1009 and upwards, everything before is fine)
Platform: Linux 4.2.0-34-generic Gitter chat room? #39-Ubuntu SMP Thu Mar 10 22:13:01 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
Subsystem: stream

Since ace1009 (#5776), stdin is truncated to the first 64kb when piped to some other stream.

Before:

$ head -c 256000 /dev/zero | ./node -e 'process.stdin.pipe(process.stdout)' | wc
      0       0  256000

After:

$ head -c 256000 /dev/zero | ./node -e 'process.stdin.pipe(process.stdout)' | wc
      0       0   65536

This also goes for piping to bl(), and the end event on process.stdin seems to be fired only when the input is smaller than 16384 bytes.