ConfigSluper cannot re-parse a file written by itself.

config file is as below:

list('XX') {
one {
a = 100
b = 200
c {
x1 = "x1"
x2

}
}

two = "2000"
}

ConfigSlurper can parse correctly. But when call its writeTo method to a file, the file like this:

list="XX"
one."list.a"=100
one."list.b"=200
one"list.x1"="x1"
onex2."list.y1"=1
"list.two"="2000"

This output file cannot be re-parsed.
The error message in stdout as below:
[list:XX, one:[list.a:100, list.b:200, c:[list.x1:x1, x2:[list.y1:1]]], list.two:2000]
XX
2000
2000
100
x1
x1
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
script13238783009061342328505.groovy: 4:
[list.x1] is a constant expression, but it should be a variable expression at line: 4 column: 13. File: script13238783009061342328505.groovy @ line 4, column 13.
one"list.x1"="x1"
^

1 error