Text Widget Bug?

Twice in the last week I have had to fix client sites that had a text widget in a sidebar. The clients originally had promotional text in the widget and everything displayed fine. When they deleted the text and left the widget blank (no title and no text), it caused the content to not display on any pages. Switching to the default theme did cause the content to appear, but on at least two other themes it did not display until I either added text to the widget or removed it from the sidebar. Is this a bug?