According to the specification http://samtools.sourceforge.net/SAM1.pdf (see "1.5 The alignment section: optional fields"), there are the following types of optional fields: 'A', 'i', 'f', 'Z', 'H' and 'B'. The last one 'B' is not parsed for some reason during reading of a BAM file (see function BamReader::AlignmentReader::read()).
Therefore an error occurs, see http://ugene.unipro.ru/forum/YaBB.pl?num=1340703459/0#0.
An automated test is required as soon as the issue is fixed!