Hopefully, I'll explain this correctly.
Environment
SAB 2.3.0 with 'Glitter - Night' skin. Viewed via FireFox 52.3.0 ESR on Debian Stretch.
I have 3 servers configured. SRV1 is priority 0, SRV2 is priority 1, SRV3 is priority 2.
All 3 are enabled.
What I did
I started by examining my current active connections in 'Status and interface options' -> [Connections] tab.
[Show active connections] is ticked. There are 3 server connection list sections shown (SRV1, SRV2, SRV3).
For the current download, only connections are being made to SRV1.
I navigated into 'SABnzbd Config' -> [Servers] then unticked the [Enabled] box for SRV1, then returned to the download queue screen.
Problem
I then clicked on 'Status and interface options' -> [Connections] tab.
There are still 3 server connection list sections shown (SRV1, SRV2, SRV3). And the connections that are now being made to SRV2 appear in the connection list box for SRV1.
Workaround
To correct this, I launched a new browser tab (and closed the old one), loaded my SAB interface again, then examined 'Status and interface options' -> [Connections] tab again. Now, there are the expected 2 server connection list sections (for SRV2 and SRV3), and the current connections are correctly shown in the list box for SRV2.
Display bug?

