Blank lines in a text frame spaced differently from other lines

A completely blank line of text in a text frame (as from typing Enter Enter) gets a different height from other lines, even a line containing a space. (In 2.2 it takes a little more space, in the 3.0 nightly it takes a lot less space.)

Is this a bug or a feature? And if it's a feature, I couldn't find any "paragraph" or "empty line" settings to control it with.

(This is on a Windows 7, 64-bit box. The particular font doesn't seem to matter; the same behavior occurs with FreeSerif, Arial, Constantia, and Times New Roman.)

Thanks!