Strange Behavior Of Format Function

Hi, I came upon a strange behavior of Format function in report, which I'm unable to explain.

I have some double value, which I want to format. E.g. the value is in db field "Users" and is 303870

1)
If I set a Value property for the field to
=Fields!Users.Value or CDec(=Fields!Users.Value)
//the value is already double so the CDec has no effect

and Format property for the field to
=Format(me.Value,"#,#") or =Format(Fields!Users.Value,"#,#")
than the number which is visible in the report is 3303,873870 ???

2)
If I put in the Value property
=Format(Fields!Users.Value,"#,#")

and the Format property is empty
than the output is ok 303,870, however this is not desired, because the value is than handled as string

3)
If I put in the Value property
=Fields!Users.Value

and into Format property
=Format(CStr(me.Value),"#,#")
than the output is ok again.

As I understand, the Format should be same as in VB (I am actually C# programmer, not very familiar with VB) so I tried to use Format in VB on double value, and the output was as expected (e.g. 303,870), but when I used to a string I got only the style (e.g. #,#).

So I wonder, the ReportingServices Format function works correctly only with string input? But why than works the example 2)? Or do I have somewhere a mistake?

Thanks for the advice.