I was inspecting the code about jobs and, unless I've misunderstood it, it seems to me that a maid doesn't just improve the condition of the mansion, but she sets it:

var temp = 5.5 + (person.sagi+person.send)*6
person.xp += temp/4
globals.state.condition = temp

So, if N maids work in the mansion, the job of the first N-1 maids is useless because the mansion condition is always overwritten by the next maid: only the competence of the last slave matters.
If this is intended, players should not be allowed to assign more than a slave to clean the mansion (at line 73, maxnumber should be = 1); if not, the mansion condition should be improved (+=).

its not a bug
globals.state.condition is "setget" to cond_set in globals.gd
temp will be added to condition through this function

You're right, but Jesus. This is not how a setter should behave. The way the setter is defined, this simple statement:

globals.state.condition += 30

is equivalent to add to the current condition not just 30, but (30 + condition). I.e. the condition is doubled and then increased by 30. :|