Backtrack over capture?

[scand1sk]

This may be a feature, but I need to backtrack after a capture and it does not seem to work.
I have this use case:
I want to parse an array of the form [a,b,c,d,…] with a, b, c being either integer or floating-point number (using standard C-like format), i.e. :

  def int_const[_: P] = P(CharIn("+\\-").? ~~ CharIn("0-9").repX(1)).!.map(i => i.toInt)

  def float_const[_: P] = P(
    CharIn("+\\-").? ~~ CharIn("0-9").repX ~~ "." ~~ CharIn("0-9").repX(1) ~~ (
      CharIn("eE") ~~ CharIn("+\\-").? ~~ CharIn("0-9").repX(1)).?).!.map(f => f.toDouble)

  def array[_: P] = P(
    "[" ~~ (int_const | float_const).rep(sep = ",") ~~ "]").!

The issue is that when I want to parse a float (e.g., 500.0), it is first parsed as an int (500), before a "." symbol is encountered instead of the expected ",". I expect that the parser backtracks and parses 500.0 as a float instead.
Is this a bug, a feature, or am I missing something?
I am using FastParse 2.1.2 and ScriptWhitespace.

[He-Pin]

why not float_const | int_const?