@Andrew Heard
I have deleted both positions from the DB, they should disappear from the system within an hour.
Actually to remove your position, it should be possible to just remove the group from the active groups of the profile while the LT is running (no need to delete the group completely). I am not even 100 % sure and I am the developer, so it is not something the user should be expected to come up with
To be honest, this is an "unexpected" side-effect of enabling the possibility for group locations to be persistent - the positions always seemingly disappeared before as each group had a timeout. Even setting the group's timeout and then switching it back to unlimited will not help.
So simply put, there is no approach to do that when you share your position to the group with unlimited position timeout, which is not exactly user friendly. There indeed should be some method to do this. Unlimited time groups are not used that much (67 so far) so you are the first one to report this logical inconvenient consequence. Sorry about that. I will write it down as an improvement/bug to be solved.
As for the date, we will not be able to help even after the fix. The date should be formatted according to your system's locale and I would expect other webs or apps to be using this format too on your device. We cannot enforce e.g. European locale on other users worldwide which might be unusual for them. There would have to be a special settings in you profile to select the prefered date/time format.