I got a ping-pong effect when I changed the name of a prioritised Logos Series in v5.1 e.g.
- change the Series name of Expositor's Bible Commentary, Abridged (EBC) in 5.1
- have to re-Prioritize EBC as the effect is to show the old series name with 0 volumes!
- after syncing, v4 shows the original Series name in Library, but shows the custom series name under Prioritize
- fix that by re-prioritizing EBC series in v4
- after syncing, v5 is Prioritized with original Series name and 0 volumes
- have to fix that by changing custom series to original name AND re-Prioritize (showing 0 vols)
- then I have to re-Prioritize v4 as that shows 0 vols after syncing.
- And then v5 also shows 0 vols...!!!!
I found that the input box didn't show that I had two spaces between the comma and "Abridged" when changing back to the original series name, because it was split over two lines as shown below:-

I know that the custom Series metadata feature is not implemented for v4, but I didn't think there would be an issue with this as the changed Series name would be sync'd to v4 as a metadata change. And the same would apply to any custom Series that I defined. ??