[This article applies only to InDesign CS4 and earlier. InDesign CS5 lets you apply vertical justification to non-rectangular shapes.]
For another edition of my Buried Treasures series, here’s a note found in the Help topic, Align or justify text vertically within a text frame.
Vertical justification isn’t applied to text that takes on a non-rectangular shape due to influences such as text frame shape, text wrap, or corner effects. In these cases, top alignment is applied. When a corner effect is applied, vertical justification is possible if you make the text area rectangular by increasing the Inset value in the Text Frame Options dialog box, relative to the Size value in the Corner Options dialog box.
In other words, vertical justification and corner effects don’t play nicely with each other in InDesign CS4. One workaround, as described in the Help topic, is to increase the inset value in the Text Frame Options dialog box (Ctrl+B/Command+B) so that it’s at least as large as the corner effect value. In the example below, I justified the text within the text frame, and then I added a 2p corner effect, and then I added a 2p inset.
That’s one option, which works perfectly well if you don’t mind changing the inset value. If you want your inset value to be smaller, the best approach is to use two frames of the same size. Apply the vertical aliignment to the text in one frame, and apply the corner effect to the other frame, and then stack and group the two frames.