Just so you don't confuse others, you mean you want your report to load in a navigation form, not navigation pane, yes? The nav pane is the pane on the left side that shows all the db objects. All I can think of is the cause for this when using forms - the textboxes had multiple lines/rows in it, such as
dog
cat
bird
That can do weird things with the data display. Maybe check yours for multiple lines with a few records. It might differ between records.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.