Forwarded message flag improperly handled

When having forwarded a message, using Thunderbird on ubuntu, an arrow is shown to the left of the subject.

However, when looking at that forwarded message using Thunderbird on Windows, there is no forwarded arrow.

Furthermore, old forwarded messages are not flagged with arrows on ubuntu, but they are when using Windows.

So, I get the impression that Thunderbird 60 does neither write the forwarded flag to the imap server, nor reads that flag or at least does not reflect its status in the user interface.

I'm using Thunderbird 60.2.1 on Ubuntu 16.04 LTS Desktop.