Access Reports are formatted in the following order and will also print the sections in the following order unless you have set the "Force New Page" property to something other than none for one of the sections.
Report Header
Page Header
GroupHeaders
Detail
Page Footer/Group Footers (Depending on how much detail)
Report Footer
Since you do not mention using a Report Header or any code then the Page Header MUST format first. You can stop the Page Header printing on Page 1 etc but you have not mentioned setting this up either.
When viewing your subreport in the design view of the report note that this is the amount of space that the sub report will take regardless of wether there is any detail or you have set the can grow can shrink properties of the items in the sub report. I take it you have nothing but detail in the Sub Report.
Sorry I cannot be of any further help.