When trying to clarify the mind about these things I find it helpful to think in these terms
The contract DEFINES what you are getting and the amount you will pay. It is firm and binding when agreed. It is in fact a promise from the seller to provide something and a promise by you to pay for it.
Where the promise can be fulfilled instantly on both sides there is no problem, but if money has to be transferred to the sellers bank and the ownership of the property has to be registered along with other legal and administrative matters there has to be a delay while these things are sorted out. In such contracts a completion date (houses etc), settlement date (shares etc) or delivery date (cars and the like) is set at which the promises are to be fulfilled and you then have title to the property and can exercise any rights that go with it.
It then follows that at time of contract you know exactly what your entitlements are but you can do nothing with them until the second step is done. (except you can of course sell on the promise to a new buyer if you want to)
If you think things through according to that principle you should almost invariably understand what the legal process is likely to be.
If the seller does not complete, settle or deliver as agreed you can seek remedy for any loss you have suffered through the courts but thats all. He has the same right if you fail to go through with your promise to pay.
Applying this logic to the points you raised:
On dividends you get the dividend if it was included in the promise but whether you get it from the seller or directly from the company depends upon the exact timing
On voting rights the simple analogy is that the seller of a house continues to live in it and decides what is done with it and done to it until the completion date He, not you, decides whether to call in the builder to seal a hole in the roof. If you dont like what he has done (or not done) you have only to prove that his action has resulted in a failure to keep his promise.