Gray ribbon across the screen in Reading Mode

[Guntis]

Open Accordance, place cursor in any commentary, press Ctrl+R to open it in Reader Mode. Select any word and press Command+Option+3. Highlighter palette opens and a gray color rectangle appears across the bottom part of the screen. When I start scrolling, middle part disappears, but both ends outside the scrolling text remain.

(MacBook Pro 17", spring 2011 model, OS X 10.9.2, the latest version of Accordance)