causas communis voti...

Hello. I am having trouble understanding this sentence. It is a law which states that donationes nuptiales cannot be reclaimed, "quando huiuscemodi causas communis uoti complendi ratio prouocet".
My guess is that the text means that the donations cannot be reclaimed because they were the cause for the other party to fulfill his marriage vow, but the grammar and exact translation of the sentence leave me clueless.
I think that ratio is the subject, provocet is the verb and causas is the object; so reason provokes such causes for fufulling the common vow?
I apologize in advance for my bad Latin (and English!)
Thank you very much
 
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