Is there a but in BWA 3'-end trimming?

[Yilong Li]

I got the following lines in the BAM file produced from BWA mapping using -q 6. It seems that the soft clipping in the CIGAR field is reporting one base less than should have been trimmed by the BWA trimming algorithm.

ILLUMINA-8C38E9_0111:3:99:15568:1908#0  83      1       9999977 60      32S50M  =       9999814 -213    GGCAGGGAGGTCCCTTGGGCCCAGGGTTTCCAGACCAGCCTGGCCGACACGGCGAAACCCCGTCTCTACAATAAATTAAAAT      #################################?:<?-?:445>-CA:@A??CDADA?=?BDEDEDEAEEEEEBEABEDE-E
ILLUMINA-8C38E9_0111:7:46:16510:9079#0  83      1       9999978 60      5S77M   =       9999740 -315    TACAGCCCAGCCTGGCCGACACGGCGAAACCCCGTCTCTACAATAAATTAAAATATTAGCTGGGCATGGTGGTGTGTGCTTG      ######?=C=CC@FDFEGBGEGGGGGFDBGGGFGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGFGGGGFGGGGGGGGGGEG
ILLUMINA-8C38E9_0111:7:86:18250:3356#0  147     1       9999985 60      33S49M  =       9999455 -579    AGACCGTGTGACACCGGGAGTAACAGCCCAGCCGGGCCGACACGGCGAAACCCCGTCTCTACAATAAATTAAAATATTAGCT      ##################################B?CFFEFDGGGGGGGEGGGFGGGGFFGGGGGGFGFFGGGGGGGGGGGG
ILLUMINA-8C38E9_0111:3:37:15542:13225#0 99      1       10000237        50      71M11S  =       10000385        230     GTTTTTTGTTTGTTTTGAGACAGAGTCTTGCTCTGTCGCCCAGGCTGGAGTGCAGTGGAGCAATCTCAGCTCACTGCAAGCC      GGDGGGGGGEDFGGGF@GGGGGGEGEGGGGGED?GDFEED>)=:5-662.0<:<5749.<81682:@?9@############
ILLUMINA-8C38E9_0111:3:53:3839:8121#0   99      1       10000270        51      81M1S   =       10000541        353     TGTCGCCCAGGCTGGAGTGCAGTGGAGCAATCTCAGCTCACTGCAAGCTCCGCCTCCCGGGCTCACACCATTCTCCTGCCCC      GGGGEGGGGGDGGFGGGEGGEFDFFFD?FFDEGGFDFFGGGGFGGGEABEEEDEACBE7-6%-23BABA5,:;;=?0-??##

Could somebody check your own BWA mapped BAM files to see if this is a general bug in BWA? Or is this a generally known feature?!