[TYPO3-english] RTE: always show table borders?

[Urs Braem]

Hi

I'm looking for a way to keep the helpful (blue, dashed) borderlines for tables in RTE active all the time.

RTE.default.buttons.toggleborders.setOnRTEOpen = 1
RTE.default.buttons.toggleborders.setOnTableCreation = 1

as on https://docs.typo3.org/typo3cms/extensions/rtehtmlarea/Configuration/PageTsconfig/interfaceConfiguration/Index.html

are doing what they can. But whenever a CE is saved, the table's borders still disappear. 
Is there no other option? TYPO3 7.6

Cheers
Urs