Hes not Suffering from a Bug I think
The Game is set to not Allow Finishing the Discard or Create or Split Army Screen when Population Limit or Ressources Limit is Exeeded.
I noticed that quite a few Times when I had more Units in my Town than Allowed thanks to the Start Quests :P
So now simple Solution
Press Create Army Screen
Move Units which are over Capacity Into that Army
Move Ressources you dont want on to that Army
Now Create Army
Make sure that Both Army and City dont exceed Caps
Promo and Quest Units if all Set together can Amount to 20 at Max
So an Army which has 60 as Max Population should be well Able to Take in the Units
You Cant Move Ressources to an Army before you put Units into it.
You Cant Create the Army when Any Limit (except Gold) is Exceeded (Gold can be Exceeded)
You Can Move Units out of Town to get below Population Limit the Units and Ressources wont be Discarded yet instead they will be Stored in the Army.
ps Hope that Helps
If it doesnt pls Answer us with the Following Infos
1. How Many Units do you have and what is your Population Cap at
2. If Possible give us a Screenshot you can Create Screenshots by Pressing F1 in the Game the Screenshot will be safed in the Game Folder
3. Give the Log1 File which is also in your Game Folder to one of Devs (For Example Joseph which answered earlier in this Thread)
In the Shadow of the Black Cross. We Fullfill our Duty in your Name.
And Look forward to the Day we Return to your side Silvanos.
Watching over our Comrades as they Fullfill their Duty in your Name.