Float bars on finished tasks

Hello planners,

can somebody please explain why Primavera P6 V7 or R8 displays a float bar when a task is completed, eventhough the Free float and Total float fields are empty?

these tasks are not out-of sequence

the float bar goes until the remaining start of the first successor in sequence

this happens for tasks wiche were critical or not critical all the same; how can it be possible to draw a float bar for a completed task?

thank you for your help and explanations

Alexandre