This discovers new anomalies in activity network under generalized precedence relations ( GPＲs) ． In conventional ideas，only two causations could result in consumptions of time floats of an activity: ( 1) the activity actively consumes time floats，and ( 2) it passively consumes time floats because of the impaction of consumptions of time floats of its preceding activities． However，we discover that even without the two causations， the time floats of an activity also can be consumed． These anomalies are hidden consumptions of activity floats，and may appear in projects with GPＲs． We study the anomalies based on activity networks under GPＲs，and design algorithms to quantize the hidden consumptions of classic total float and hidden float respectively． The hidden consumptions of activity floats may weaken current models and optimization approaches based on time floats so that has indispensable application to project scheduling with GPＲs．