I also found that red(hsv(90, 100%, 50%)) returns 63.75 where i expect an integer.

#408000; = hsv(90, 100%, 50%) and red(#408000); indeed returns 64.

Update: i found that the hsv value should be 50.2%, but also red(hsv(90, 100%, 50.2%)) gives 64.005 and not an integer

@bassjobsen HSV of #408000 is actually [90, 100%, 50.19607843%] (rounded to 8 digits after .).
And not-rounded RGB of hsv(90, 100%, 50%) is [63.75, 127.5, 0]. Less rounds colour values when they output to CSS properties (going deeper than 8 bit and rendering rgb(63.75, 127.5, 0) instead of #408000 would not make much sense). So I don't see any issue in this case.

In other words:

@c: hsv(90, 100%, 50%); // color object = rgb(63.75, 127.5, 0)
r: red(@c);             // "some" floating point number
c: @c;                  // CSS color value = #408000

@seven-phases-max, thanks for your clear explanation. In that case at least the docs don't seem to be correct.

http://lesscss.org/functions/#color-channel-red:, returns an integer 0-255.

In the code for instance hsvhue does a color.toHSV() first. For red() the color object is not "cast" to a rgb object which only can contain integers.

Yes, the documentation may be not always up-to-date.

For red() the color object is not "cast" to a rgb object which only can contain integers.

Color object is an RGB object and it may contain non-integer values actually:

r: red(rgb(1.23, 0, 0)); // = 1.23