Genghis,
If what you have just said about positive lateral stability causing roll into sidslip is true, then everyhing I have ever told my students about this subject is untrue. (This is of course entirely probable, as most of them subsequently passed their JAR ATPL exams).
Do you not mean that positive directional stability causes yaw into sideslip? If the aircraft in question yaws into sideslip to a greater extent than it rolls away from it, this might explain the phenomon described in the original question. (I have avoided the concept of one mode of stability being dominant, because this has caused some controversy in this forum in the past).