Bi-directional field-aligned electron distributions are sometimes observed in the plasma sheet. We looked through AMPTE-IRM data at high time resolution to study their appearance in the high-beta plasma sheet between 10 and 15 Re. We found that the occurrence frequency of bidirectional distributions drops sharply at r less than or equal to 15Re. We did not observe such anisotropic distributions in the undisturbed plasma sheet, but found them in the locally disturbed central plasma sheet preferentially in the flux tubes with low density and strong magnetic field. No simple association with a specific magnetotail state or substorm phase or rapid flows were observed, but opposite to expectations the largest field-aligned anisotropy values have been attained during strong magnetic pulse events characterized by the largest magnetic field compression (Bz greater than or equal to 15 - 20 nT) in which the perpendicular temperature decreased instead of being increased. We study such events to show their identity with plasma bubbles and discuss the reasons why the betatron acceleration is not as effective as Fermi acceleration in these cases. The observations are interpreted in terms of underpopulated newly-reconnected plasma tubes of limited cross-tail extent (plasma bubbles) which are produced by impulsive magnetic reconnection and transported to the inner magnetosphere.