Filebeat appending new lines even if there is change only in existing line

[Yenike_Raghu_Ram]

Say like in original file I ve 2 lines
a
b
We've modified one line say 'a'
now output file in logstash is like
a -- original data
b
a -- modified data
b
I am expecting it to be like log file to have only two lines as with my original log file which has two lines , but with modified data in one of lines
a -- modified data
b

Following is my filebeat prospectors and log stash conf

filebeat.prospectors:

• type: log
  paths:
  • directory/*.html
    output.logstash:
    hosts: ["ipaddress"]

input {
beats {
port => 5048
}
}
output {
stdout { codec => rubydebug }
file
{
codec => line {
format => "%{[message]}"
}
path => "C:/Program Files/logstash-6.2.3/testPractice/LogsCollected/DebugLog09May2018/OneTwo.html}
}

Attached original file and log stash file observe that in log stash file for each every change in line all lines are appended

[kvch (Noémi Ványi)]

What do you see instead of the expected output?