Two voices notation error

MuseScore 0.9.5 R2012
WinXP Media Center V5.1 SP3

A nagging error in the notation for two voices. When the example is opened, measure s 57, 59, 63 and 65 erroneously show duplicates for the first notes of the two voices in these measures. When one pushes the notes together in measure 57, measures 59, 63 and 65 are also corrected (!) A printed output reflects the corrected copy. But when saved and reopened, the measures show the error again. Probably has something to do with the 8va starting at the end of measure 56.