Yes, that is the problem.

   DB<27> x $start
 0  0.6
   DB<28> x $store->[3]
 0  0.6
   DB<29> x 0.6 == $start
 0  ''
[download]

jeroenes, repeat the above and do "x $start-0.6" and you may be enlightened.

Update: So we all can take part in the fun:

  DB<1> $x=0.6
  DB<2> x ($l,$h)=unpack"L*",pack"d",$x
0  858993459
1  1071854387
  DB<3> x $y=unpack"d",pack"L*",$l+1,$h
0  0.6
  DB<4> x $z=unpack"d",pack"L*",$l-1,$h
0  0.6
  DB<5> x $y-$x
0  '1.11022302462516e-016'
  DB<6> x $x-$z
0  '1.11022302462516e-016'
  DB<7> x $y-$z
0  '2.22044604925031e-016'
  DB<8> x unpack"d",pack"L*",$l-4,$h
0  0.6
  DB<9> x unpack"d",pack"L*",$l-5,$h
0  0.599999999999999
  DB<10> x unpack"d",pack"L*",$l+4,$h
0  0.6
  DB<11> x unpack"d",pack"L*",$l+5,$h
0  0.600000000000001
[download]

Welcome to floating point.

        - tye (but my friends call me "Tye")