Korean text is not allowed in Making Custom Column action

It is same as your picture

Column-name part is ok, But when I type any korean text in the column-function part, the error occurred.

For example, when I try to type Korean alphabet "ㄱ" in "금액", then error occured like this picture.

And 1 more alphabet "ㄱ" added as "ㄱㄱ".

( type "ㅅ" then "ㅅㅅ" & error message pop-up

/ type "ㅇ" then "ㅇㅇ" & error message pop-up

/ type "ㅕ" then "ㅕㅕ" & error message pop-up

/ type "ㅏ" then "ㅏㅏ" & error message pop-up)

This is the sample code.

let
원본 = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjQyNjE1U4rVgTAtTKFME1MLQzDTzNTEwtAYzLQ0NTc1g4gamgN1WSjFxgIA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [금액 = _t]),
#"변경된 유형" = Table.TransformColumnTypes(원본,{{"금액", type number}}),
#"추가된 사용자 지정 항목" = Table.AddColumn(#"변경된 유형", "평가", each if [금액] >= 900000 then "높음"
else if [금액] >= 600000 then "중간"
else "낮음")
in
#"추가된 사용자 지정 항목"