Minutes come out with wrong value unless you explicitly change the minute selector

[ferna‏]

I use a coarse granularity (15 minute intervals) for selecting
minutes, using :minute_interval=>15
When the date selector comes up, it shows the current time of day,
with the minute selector positioned at the 15 minute interval just
before the current time, i.e. if now it is 10:56, it comes up as
10:45, which is fine.

The problem is that if you do not make an explicit change to the
minute selector, but only modify say the date and the hour,
calendar_date_select returns the minutes as 56, not 45, which is quite
annoying, since the user expects it to return what he/she sees in the
form. Any ideas how this can be fixed?