It is not a real bug, just an advice. On my machine (Ubuntu 14.04 64 bit, Matlab R2015 b), it turned out that the ipopt.m file shadows the mex function ipopt.mexa64 which results in an error. I know, that it shouldn't be the case as the mex files should be evaluated before the .m files. But this issue can easily be fixed by renaming ipopt.m to e.g. ipopt_MATLAB.m as it is just a pure comment file and not a wrapper for the mex function.
It is not a real bug, just an advice. On my machine (Ubuntu 14.04 64 bit, Matlab R2015 b), it turned out that the ipopt.m file shadows the mex function ipopt.mexa64 which results in an error. I know, that it shouldn't be the case as the mex files should be evaluated before the .m files. But this issue can easily be fixed by renaming ipopt.m to e.g. ipopt_MATLAB.m as it is just a pure comment file and not a wrapper for the mex function.