Sounding rocket Terrier-Malemute 29.007 was launched over a 40 kR quiet auroral arc at 0813 UT on March 9, 1978. Payload instrumentation included a single-axis double probe electric field detector. The reduced data from this detector are modulated by a square wave which is coherent with the diagnostic float-bias cycle of the detector for the last ~80 s of the flight when the analysis is carried out under the assumption that E⋅B=0. This modulation may be removed by assuming that a time-varying, vehicle-generated apparent parallel field was present during the periods when the probes were floating. Three possible models for the effect were considered: a gradient in the nonthermal probe current, a gradient in plasma temperature near the rocket, and a variable dipole moment of the wake. There are significant problems with all these models. On balance, the third one appears to be the most likely. The observed effect may account for some previously reported measurements of low altitude parallel fields. It must be stressed that it cannot account for all such reports.