New var creation with right bit shift shows incorrect result using same initializer

Yepp, it's rounding and bitwise operations, simplest repro is
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0.99999999999999995 & 1

Results:

// Firefox and Chromium:
> 0.99999999999999994&1
0

> 0.99999999999999995&1
1

> 0.99999999999999996&1
1

// Espruino:
>0.99999999999999994&1
=0

>0.99999999999999995&1
=0

// It's ok just a bit higher:
>0.99999999999999996&1
=1

Edit: with @Robin's numbers:

// In browser:
> var val = 915E6;
> var newVal = val * Math.pow(2, 19);
> var newDiv = newVal / 32000000
> {val, newVal, newDiv}
{val: 915000000, newVal: 479723520000000, newDiv: 14991360}
> (newDiv-14991360)*1e9
0
// Exactly 0 in browser

// Espruino:
...
>newDiv-14991360
=-0
>(newDiv-14991360)*1e9
=-1.86264514923
// not exactly 0!