[GENERAL] streaming replication - crash on standby

The last line from pg_xlogdump of the last WAL file on the crashed standby server shows the following.

pg_xlogdump: FATAL:  error in WAL record at DF/4CB95FD0: unexpected pageaddr DB/62B96000 in log segment 00000000000000DF0000004C, offset 12148736

I believe this means the standby server received WAL file out of order?  But why did it crash?  Is crashing normal behavior in case like this?

Thanks,

Seong