Landing and sinking speed...?

Hi,I encountered a curious thing just a moment ago:I was on final to EDDF 25L and everything was set as normal - both CMD's on, A/Thrust, ils frqs and courses for both cpt and F/o and so on. Around 1800 RA I saw that speed was gradually sinking below the ref speed ( 144kts/flap 30) and continued to do so to the yellow and red tape until the plane stalled and crashed. So a kind of autolanding :) Petteri PulkkinenEFNU