Commisions-for-historical-index-exits-seem-to-be-too-low

What's the bug precisely? You can set commissions to just about anything you want. Let's start with how you've set yours. Preferences > Backtest > Commissions...

The commisions for the long position are ok from my point of view, only the close of the positions seem to have a problem

Now I see what you mean. These are "Historic Index Exits", i.e., not a result of a strategy trade, so that's the difference. Let's see if Glitch has an idea about changing that.

Is is it a bug or a feature?

Since a [minimum] commission is being applied, I think it's a bug. We're tracking it.