shift on stream does not work on task built using chronograf

Hi
First, thanks for creating such an amazing stack, it's truly astoundingly good.

I've been trying to set up alerting using kapacitor streams and have been tearing my hair out for 2 days. I have previously successfuly created a batch query that compares a current mean value with the same mean value from an hour previous...the guts of it is this :
```
var past = batch
|query('select mean(traf_i_total) from "network_summ"."thirty_days".network_summ')
.period(1m)
.every(30s)
.offset(1h)
.align()
.groupBy(*)
var current = batch
|query('select mean(traf_i_total) from "network_summ"."thirty_days".network_summ')
.period(1m)
.every(30s)
.align()
.groupBy(*)
```

...and it works a treat

However when I try to so the same thing with stream data the values from "past" are always the same as the values from "current". I've even tried using chronograf to create the following task(and added the writebacks to the "backtest" db as I found in an example), but the results clearly show the values are the same.

the tickscript is :

```
var db = 'network_summ'

var rp = 'thirty_days'

var measurement = 'network_summ'

var groupBy = ['endpoint']

var whereFilter = lambda: TRUE

var period = 1m

var every = 1m

var name = 'madness'

var idVar = name + ':{{.Group}}'

var message = ' {{.ID}} {{.Name}} {{.TaskName}} {{.Group}} {{.Tags}} {{.Level}} {{ index .Fields "value" }} {{.Time}}'

var idTag = 'alertID'

var levelTag = 'level'

var messageField = 'message'

var durationField = 'duration'

var triggerType = 'relative'

var shift = 1h

var crit = 0.001

var data = stream
|from()
.database(db)
.retentionPolicy(rp)
.measurement(measurement)
.groupBy(groupBy)
.where(whereFilter)
|window()
.period(period)
.every(every)
.align()
|mean('traf_i_total')
.as('value')

var past = data
|shift(shift)

var current = data

var trigger = past
|join(current)
.as('past', 'current')
|eval(lambda: abs(float("current.value" - "past.value")) / float("past.value") * 100.0)
.keep()
.as('value')
|alert()
.crit(lambda: "value" > crit)
.stateChangesOnly()
.message(message)
.id(idVar)
.idTag(idTag)
.levelTag(levelTag)
.messageField(messageField)
.durationField(durationField)
.log('/var/tmp/madness.log')

trigger
|influxDBOut()
.database('madness')
.create()
.retentionPolicy('autogen')
.measurement('backtestvals')
.tag('query', 'joined')

past
|influxDBOut()
.database('madness')
.create()
.retentionPolicy('autogen')
.measurement('backtestvals')
.tag('query', 'baselineAvg')

current
|influxDBOut()
.database('madness')
.create()
.retentionPolicy('autogen')
.measurement('backtestvals')
.tag('query', 'currentAvg')
```

and the output in the backtestvals db :

```
> select * from backtestvals where endpoint='jp89667-tok-9888' or endpoint='de27341-fra-9876' or endpoint='fr19556-par-9874' order by time asc;
name: backtestvals
time endpoint query value
---- -------- ----- -----
2018-03-30T12:35:00Z jp89667-tok-9888 currentAvg 1924.25
2018-03-30T12:35:00Z de27341-fra-9876 currentAvg 2160.4285714285716
2018-03-30T12:35:00Z fr19556-par-9874 currentAvg 2218.875
2018-03-30T12:36:00Z de27341-fra-9876 currentAvg 2219.529411764706
2018-03-30T12:36:00Z fr19556-par-9874 currentAvg 2523.266666666667
2018-03-30T12:36:00Z jp89667-tok-9888 currentAvg 2393.3333333333335
2018-03-30T12:37:00Z fr19556-par-9874 currentAvg 2206.4
2018-03-30T12:37:00Z jp89667-tok-9888 currentAvg 2175.35
2018-03-30T12:37:00Z de27341-fra-9876 currentAvg 2154.65
2018-03-30T12:38:00Z jp89667-tok-9888 currentAvg 2270.5
2018-03-30T12:38:00Z de27341-fra-9876 currentAvg 2519.133333333333
2018-03-30T12:38:00Z fr19556-par-9874 currentAvg 2232.4117647058824
2018-03-30T12:39:00Z de27341-fra-9876 currentAvg 2145.9473684210525
2018-03-30T12:39:00Z fr19556-par-9874 currentAvg 2256.3684210526317
2018-03-30T12:39:00Z jp89667-tok-9888 currentAvg 2286.2105263157896
2018-03-30T13:35:00Z fr19556-par-9874 baselineAvg 2218.875
2018-03-30T13:35:00Z jp89667-tok-9888 baselineAvg 1924.25
2018-03-30T13:35:00Z de27341-fra-9876 baselineAvg 2160.4285714285716
2018-03-30T13:36:00Z jp89667-tok-9888 baselineAvg 2393.3333333333335
2018-03-30T13:36:00Z de27341-fra-9876 baselineAvg 2219.529411764706
2018-03-30T13:36:00Z fr19556-par-9874 baselineAvg 2523.266666666667
2018-03-30T13:37:00Z de27341-fra-9876 baselineAvg 2154.65
2018-03-30T13:37:00Z fr19556-par-9874 baselineAvg 2206.4
2018-03-30T13:37:00Z jp89667-tok-9888 baselineAvg 2175.35
2018-03-30T13:38:00Z fr19556-par-9874 baselineAvg 2232.4117647058824
2018-03-30T13:38:00Z jp89667-tok-9888 baselineAvg 2270.5
2018-03-30T13:38:00Z de27341-fra-9876 baselineAvg 2519.133333333333
2018-03-30T13:39:00Z jp89667-tok-9888 baselineAvg 2286.2105263157896
2018-03-30T13:39:00Z de27341-fra-9876 baselineAvg 2145.9473684210525
2018-03-30T13:39:00Z fr19556-par-9874 baselineAvg 2256.3684210526317
>
```
I've been thru the docs and looked at lots of examples so I guess I must be misunderstanding something :(

I am using influxdb 1.3.7, Telegraf 1.5.2 and Kapacitor 1.4.0

any pointers greatly appreciated

Many Thanks !!

Steve

Start with the posted TickScript, especially the window, shift, and join branches, and compare the currentAvg and baselineAvg backtestvals output. Reproduce the task using the shown InfluxDB, Telegraf, and Kapacitor versions, then verify that baseline values represent the one-hour-shifted stream rather than the current stream.

Written by the indexing model from the issue text.