In NAV 2013 R2, if a RecordRef does not have a active record, CURRENTKEYINDEX will return -1. IN NAV2009 and older, the value was 1 (As the number of the primary key).
If the value of CURRENTKEYINDEX is given to KEYINDEX – a index out of bounds error will occur.
This is not documented in the NAV 2013 R2 help.