Maddening problem with frame below

[Steve Rickaby]

I wonder if anyone can help me with an inexplicable irritation.

I have a para format with an under-rule graphic taken off the reference page and applied with the Frame blow pgf feature in the Advanced pane of the para designer.

When the format is initially applied to the para, the rule appears correctly. Left to its own devices, however, (no, I don't know, maybe during book update), the rule suddenly appears about 18 points below where it should be, in fact in the middle of the next line below.

When I re-apply the format to the errant para, the rule snaps back to where it's supposed to be.

Any ideas?

-- 
Steve