newbie's question mdx

I have two queries:

select 
{[Measures].[Title played amount]} on 0
,
nonemptycrossjoin(
tail([Date Dim].[Days].[Month Day],30).item(0):
tail([Date Dim].[Days].[Month Day],1).item(0),
[Date Dim].[Calendar].[All],
2
)
on 1
from
[My Cube]

and

select 
{[Measures].[Title played amount]} on 0
,[Date Dim].[Calendar].[All] on 1
from
[My Cube]
where
tail([Date Dim].[Days].[Month Day],30).item(0):
tail([Date Dim].[Days].[Month Day],1).item(0)

The second acts as if there was no where clause. Why do they return different results or what may be the reason of that situation?

Thx, in advance

Rafal