Since the elastic5 upgrade the dumpIndex script seems to produce partial dumps :
dcausse@wasat:~$ mwscript extensions/CirrusSearch/maintenance/dumpIndex.php --wiki enwiktionary --indexType content | pv -i5 -l | wc -l Dumping 5102492 documents (5102492 in the index) 1.02M 0:38:38 [ 440 /s] [ <=> ] 1020500
5102492 docs must be dumped but the script produces 1M lines, given that we have 2 lines per doc it's only 500k docs.