Museum Level decreases when expeditions sent out

[Jaggid Edje]

For a few days now I've noticed my museums' level decreases by 1 on and off and I figured out that it is happening when I send out an expedition that has several of my higher level staff going out.

I feel like staff that is still employed should be included in the calculation of museum level, regardless of the fact that they are away on expedition. Is this a bug, or is it actually intentional?