Hello,
no, sorry it's not possible to go back to the v0.79, but there was no engine change in the v0.80, so they should both work in the same way.
Could you send me a Bug Report, including your Tennis.ini ? (HowTo =>
topic5-31732.php )
I guess you cannot do it from the game, so do it manually.
Then rename Tennis.ini to Tennis.ini.bak and launch the game ; it may fix the issue.