_EVENTDATES_LOCAL shows date twice for single day events

This was asked once before here: https://www.ads-software.com/support/topic/_eventdates_local-always-shows-begin-and-end-date/, without receiving an answer though.

I have that problem too now.
A customer of mine has mostly events that last 1 – 2 hours
She now wanted to always display the date and time related to the timezone of the viewer, since she started doing more online events these last years.
So I replaced all instandes of #_EVENTTIMES with #_EVENTTIMES_LOCAL and all instances of #_EVENTDATES with #_EVENTDATES_LOCAL.

That had the effect of displaying every date twice, as if there was a different start and end-date, like “Monday, 20/09/2021 – Monday, 20/09/2021”.

At first I thought I had mixed up some format somewhere, but whenever I switch back to #_EVENTDATES for some list, it will display correctly again.

What might be the problem here?

Thanks in advance!

Bastian