Affected versions]
release 77.0a1,
beta 78.0b8 (64-bit),
nightly 79.0a1 (2020-06-17) (64-bit)

[Affected platforms]
( macOS 10.14 (Mojave))

[Steps to reproduce]

1- Launch the Firefox Browser and visit https://en.wikipedia.org/wiki/Game_of_Thrones or https://www.w3schools.com/html/html_tables.asp
2- Open https://docs.google.com/spreadsheets and https://onedrive.live.com/, as well as a WYSWYG editor such as http://results.totallympics.com/forum.php?mod=post&action=newthread&fid=37
3- Open online html editor such as https://html-online.com/editor/
4- Select table from 1st step and copy in online editor in step 3
5- Select any desired amount of rows from the table in online editor, and copy.
6- Paste it in open tabs (from step 1 and 2)
7- Notice that table is pasted almost successfully only in one drive spreadsheet (notice that the information of just one row is displayed in 3 rows ) but other speadsheet will just copy one single line.

[Expected result]
rows should be pasted accordingly

[Actual result]
Selection pasted is not correct.

If repeating steps in chrome this won't occur as selection and copy works differently.

This is a bug of an older TinyMCE version. See bug 1646457#c7. With a more recent TinyMCE version (e.g. https://www.tiny.cloud/docs/demo/full-featured/) this works.