Maintenance&Training and Preparedness costs skyrocketing.

[Balthagor]

K, mystery solved...

When you deactivate your last missile fabrication (the place where the game assumes missiles to be stored) you pay a higher maintenance on all reserved missiles. This was an early design decision but as there was no feedback to the player about either the cause or the effect, this surcharge will be removed with update 7.

Until then: activate one missile fab.