Prisoners won't get assigned to solitary cells that are set as a custom sector

[Donkieyo]

I want to have for example a block of solitary cells which only min and med sec prisoners should be thrown in, however when setting them as a custom sector for min and med, prisoners won't get assigned to them and instead will wait in their cell for a solitary cell which they belong to be freed up.

It works as expected if I make a solitary cell only min or only med sec, but the custom sector feature does not work.