build() brings different results on repeated calls

[Kris-sbor]

from barcode import Code128
ean=Code128.get("1170773")
ean
<Code128('1170773')>
ean.build()
['110100111001100010010010110000100111101110101011110111011001011100111010001101100011101011']
ean.build()
['110100100001001110011010111011110100111001101001100010010000110100101101110001100011101011']
ean.build()
['110100111001100010010010110000100111101110101011110111011001011100111010001101100011101011']
ean.build()
['110100100001001110011010111011110100111001101001100010010000110100101101110001100011101011']