Problem with plotting time histograms

I am trying to plot time histograms, i.e. histograms of absolute-time data. histogram works when I use one month (1o) as the bin width:

gmt histogram EventTimes.dat -JX3iT/1i -R2008-01-01T/2008-02-20T/0/250 -T2008-01-01T/2008-02-20T/1o -BESn -Bya100f50+l"Event num." -Ggray -W1p,black

but makes a blank plot when I use a smaller bin width (e.g., 7d):

gmt histogram EventTimes.dat -JX3iT/1i -R2008-01-01T/2008-02-20T/0/250 -T2008-01-01T/2008-02-20T/7d -BESn -Bya100f50+l"Event num." -Ggray -W1p,black

My input file is attached below. Is there any problem with my syntaxes or is this a bug? Thanks!

Tianze

EventTimes.dat (41.7 KB)