Takeo... Yes, having two Wonders that are flagged to do the same thing can cause problems.
Wonders are programed to be Separate, Special, One of Kind Additions.
In my experience, the programing for Wonders may not "understand" and You can have problems if you try to place two Wonders that are the same or in other words, Duplicate Wonders.
If you have Two different Wonders and flag both to do the same thing, it can cause problems even if each Wonder does something different as well as the same thing. This depends on the importance of what the Wonder is intended to accomplish... Programing.
You can get away with having two Wonders do some things the same provided the Wonders are not duplicates of an exclusive Wonder that is intended to be the only Wonder that accomplishes what it is intended to do. Good Luck understanding the programing concerning this.
If a Civ builds two Wonders that place a Barracks in every city, it will not duplicate the Barracks but if the Civ lost the 1st Wonder, they will still have a Barracks in every city due to the 2nd Wonder that also places a Barracks in every city.
You can have Wonders do some minor things the same and get away with it but in general, if you want to be safe, keep Wonders separate and one of a kind.
...As it has been said : "there can be only one" and again, Good Luck understanding the programing for Attributes you can and cannot duplicate with Wonders
