Legal Question in Landlord & Tenant Law in Missouri

Generally, Courts allow landlords and creditors to apply funds to the oldest debt. If you owed late fees, then the next money they recieve will get applied to the late fees. However, if you simultaneaously pay the current debt, you should not incure new late fees. You did nto indicate if the money order to you designated as for late fees arrived by the time your new payment was due. If the late fee was small ( less that 25% of the normal payment) than there probably should not have been a late fee for the partial payment, that you designated as the new month's rent. If they do charge afull late fee, then keep th all the documents relatiing to that . If the landlord later wants to evict you or not return your full deposit, this bad act may help you sway the judge in the close calls on those issues.

Good luck