So I noticed this today when using squads of 8, I don't know if it applies to squads of other sizes but it probably does.
Here is an example of what happens.
A squad of 8 with 80 hitpoints gets into a fight, it wins but takes 5 dmg. There are still 8 members, but 75hp. Due to the experience earned the squads hitpoints increase to 120. Now you'd think it's hitpoints would now be 115/120 with 8 members, but instead it is 75/120 with 5 members. 3 guys just got killed 'cause the squad got more powerful, awesome. If the squad had been at full health (80/80) the upgrade will make it 120/120 with 8 members. The bug only seems to apply to damaged squads.
It gets worse.
You run your squad home to a city to heal, cause it's now down to around 60% health (75/120), BUT a city adds 100% hp to its defenders, which DOES NOT mean you now have 150/240hp, but instead 75/240 hp and BAM, your down to 3/8 squad members so 2 guys got killed by over-zealous loved ones who were so pleased to see them make it home that the smothered them with love.
Now to be fair I have noticed that if you leave the city once your hp reaches 120/240 you are fully healed on 120/120, BUT you only have 4 squad members. In order for your squad to reach its full number of 8 you have to wait for its HP to reach 240/240.
My squads currently heal 5dmg a turn. I took 5dmg at the beginning of this example. I have to wait (240-75)/5 = 33 turns for my squad to reach 8 members again WHEN I DIDN"T LOSE A MAN!
Anyone else think this is odd. Really enjoying the game now I've kinda figured out what's going on but this is a pretty epic fail.
To be fair I don't know if the squad number is purely graphical or if it affects the combat math, but I built a squad of 8, so I want 8 pls sir.
I've noticed this playing the campaign, I haven't reached a level high enough in a sandbox game to verify it.
PS. It would be awesome if the campaign quest (i.e. the MAIN quest) was listed under the quests tab of the kingdom report, just an idea, use it, don't use it.