Building a troop building reduces levy.

[Keinwyn]

Building any building that gives additional troops will reduce that troop type in that barony's levy to 0.

So for example, a small stable upon completion will reduce the light cavalry count to 0.

Note: this is on completion of the building, not the beginning.

 

[BlckKnght]

I believe this has been reported before and confirmed to be WAD.

What's actually happening is a bit subtle. When your stable completes, it increases the size of the garrison (in addition to the number of cavalry levies you can train). Garrison duty takes precedence over levy duty, so some of your existing cavalry levies (or even all of them!) get turned into garrison troops. You don't actually lose troops overall, they just change roles. Over time new cavalry will be trained up and you'll have more than you started with.

I hope this helps make sense of the situation!

 

[K-vald]

I can confirm what BlckKnght writes. They will eventually fill up and you'll have your new levy force at your command!

 

[Keinwyn]

Ah, I see now, thanks.

Makes it an interesting decision whether to build or not now... I cut reinforce rate to 1/5 of what it was.