Duplicated logs from logstash after append logs

"on my test I opened the file and then modify it appending logs. "
Step 1 : mylogs.log -> empty
Step 2 : open file mylogs.log -> add new log in the file -> save file
<dialogue> <server>localhost</server> <duration>165</duration> <outgoing><qvs_message appstate="getAPPSTATE_0"></qvs_record></qvs_message></outgoing> </dialogue>
--> mylogs.log = 1 Log
logstash (or filebeats) is reading the file the I can verify it with kibana and I have 1 log
Step 3 : open file mylogs.log -> add new log in the file -> save file
<dialogue> <server>localhost</server> <duration>165</duration> <outgoing><qvs_message appstate="getAPPSTATE_1"></qvs_record></qvs_message></outgoing> </dialogue>
--> mylogs.log = 2 Log
logstash (or filebeats) is reading the file the I can verify it with kibana and I have 3 logs but Iextected 2 logs

I hope this is well detailed