Adding rows at the end with .addRows() with false insert option in table not works as it should

[CyberNinja2007]

Today I noticed my table in sheet is 1000+ rows and first 900 or around is clear and only last 100 rows were with data I needed.

In .addRows method I noticed rows sending with !A{this._headerRowIndex}, by defaut it's A1 as I can think, so I sent a request by my own to a new test table like that:

https://sheets.googleapis.com/v4/spreadsheets/125MYdZ2eaxOi_QGUEaviH-aDMX6JWEHSRAVLp3f-ebI/values/'%D0%B4%D0%B5%D0%BA%D0%B0%D0%B1%D1%80%D1%8C'!A1:append?valueInputOption=USER_ENTERED&insertDataOption=OVERWRITE&includeValuesInResponse=true

And it ignored the first clear row and added the data at the bottom of the table. After, I cleared all rows without deleting them and sent the request again. The clear rows were ignored again and the table has new rows at the bottom.

After that I tried send the request from A1 to A2 like that (before cleared the rows again):

https://sheets.googleapis.com/v4/spreadsheets/125MYdZ2eaxOi_QGUEaviH-aDMX6JWEHSRAVLp3f-ebI/values/'%D0%B4%D0%B5%D0%BA%D0%B0%D0%B1%D1%80%D1%8C'!A2:append?valueInputOption=USER_ENTERED&insertDataOption=OVERWRITE&includeValuesInResponse=true

And it worked, the data now sends from the row I need or the first clear row. So, maybe we need to make !A{this._headerRowIndex + 1} ?

The table is test and you can try it by your own.