Nested Subreport Causing The Parents Last Header To Expand. Why? How To Fix?

I have created a "parent" table with various columns and added an extra detail row to drop a nested subreport into the table passing parameters into the sub in order to obtain the child subreport. The problem is that the the while I can line up the columns in the sub report with the parent report,

I observe something like this:

parent columns:

a b c d e f

child columns

a b c d e f

The problem is in the last column of the parent "f" it appears stretched out for some reason-about an inch even though can grow is set to false.

Its like the child is forcing the parent's last column to expand yet when i observe the border around the table in the child the "f" is clearly more narrow than the parent's f despite my matching the column widths in the layout exactly the same . In preview mode, the parent's last column is extended width-about an inch more was added. Note I tested it with No data in the child's last column and it still expands the parent column by that inch.

Also note when I dropped the subreport into the parent report I'm merging the cells on the detail row that the subreport fits across columns a, b, c, d, e, f.

So even though the subreports data lines up properly under a, b, c, d, and e; the parent's "f" still expands outward.

Any clues or suggests on what I should consider changing. I'm stumped.