  We investigate the statistical properties of the EBS order book for the
EUR/USD and USD/JPY currency pairs and the impact of a ten-fold tick size
reduction on its dynamics. A large fraction of limit orders are still placed
right at or halfway between the old allowed prices. This generates price
barriers where the best quotes lie for much of the time, which causes the
emergence of distinct peaks in the average shape of the book at round
distances. Furthermore, we argue that this clustering is mainly due to manual
traders who remained set to the old price resolution. Automatic traders easily
take price priority by submitting limit orders one tick ahead of clusters, as
shown by the prominence of buy (sell) limit orders posted with rightmost digit
one (nine).
