You don't have any rows or columns on that sheet, I'll bet.
Create some bogus calc with a value of "A". that's it. Just "A". Then put it on rows. Then unmark "show header" for it. Your chart will look just like it did before, but now it actually has an "official" row that will go away when the sheet gets hidden.
Let me know how that goes. If it doesn't take care of it, post a sample workbook and I'll help you out with that.
Oh, and also be sure not to have a title displayed. If you have a title, the sheet will still exist, even if there are no rows to display.
Man, you guys are good!
That was it. The one sheet...the one that hid correctly, had a measure as both a row and column (it was a scatterplot). The other chart just had a measure on rows...and nothing on columns. I added a bogus calc on columns and now it hides.
Oh, the nuances of Tableau. Someday I'll learn them. Thanks Joe!