Why does this oak dislike rhododendrons?

Some animosities in the botanical world make perfect sense. Tomatoes and their relatives hate growing in the vicinity of walnuts because of the juglone, but why does my shingle oak so despise the rhododendrons that grow in its shade and benefit so greatly from its accumulated leaf litter? Because of the clay content and high pH, not to mention frigid temperatures, late summer droughts, and desiccating winter winds, rhododendrons and similar semi-soft, acid-loving plants are difficult to grow here in Lincolnland, and having found a near ideal protected setting for a rhododendron bed beneath a large oak at the east end of the house, our spring display of azaleas and rhododendrons is about as good as it gets in this area. So why does this oak drop a constant barrage of limbs upon the defenseless shrubs below? Is it floral display envy? They can hardly be a worthy competitor, and yet every year one or more of the rhododendrons will get maimed, mauled, or crushed by oak limbs. Maybe this oak just has a mean dark streak deep in its heartwood, and having already had a near miss myself, the Phactor suggests that you admire the rhododendrons from a safe distance just beyond the spread of this oak's crown.