Maybe a rounding error?

[StuartIanNaylor]

The main transformer snippet of my code is

  t  pad = (1 - duration)
  startpad = abs(pad * pad_offset) / 2
  endpad = 1 
  tfm1.pitch(pitch_offset)     
  tfm1.tempo(tempo_offset, 's')
  tfm1.pad(startpad, endpad)
  tfm1.trim(0, 1)
  tfm1.build_file('temp.wav', filename + '-av-' + str(x) + '.wav')

The main thing is the last tfm1.trim(0, 1) as the output from soxi -D

0.999938
pangram1029-av-17.wav
0.999938
pangram1029-av-18.wav
1.000000
pangram1029-av-19.wav
0.999938
pangram1029-av-1.wav
0.999938
pangram1029-av-20.wav
0.999938
pangram1029-av-2.wav
1.000000

Why does that final trim sometimes (not always) and how does soxi -D get a fraction of the sample rate 15999.008 samples = 0.999938 sec @ 16kSR ?