What I did:
open an email-link I created. Agenda is in full screen mode
the email flashed briefly (< 1 sec) in split-screen view along side Agenda, then the mail-window dissapeared. Agenda dropped out of full-screen mode.
The email is in full-screen mode in a new workspace so I have to go there to read it and when back in Agenda, re-enter full screen mode.
What I expected:
That Agenda remains in full-screen view. And that the email shows in a split-screen alongside Agenda in the other split-screen. It is fine if the email shows in the Mail app, as a standard size Mail window (or, when Mail is in full-screen mode also, in split-screen within the Mail app).
Things that might be helpful to know (Agenda version, OS and model, etc):
Agenda notes version 6.0.1; OSX 10.14.6, MacBook Pro 13” late 2012.
There is no difference to Mail being full-screen mode or not, it is consistent with Agenda in full-screen mode.