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MatrixRank[m, Modulus -> 5] is broken


I have a strange problem.
I ask for MatrixRank of matrix over the reals without Modulus and I get some number, assume 5;

next I add a raw into this matrix and ask for the rank and I get 5;

next I do both calculations using Modulus -> 7 and get 4 and 5.

There is a problem!!! 
if a the additional raw was linear depended over the reals, it m-u-s-t be linear depended over Modulus because a linear combination for this extra row using other rows is valid when we apply Modulus -> 7.
Therefor I suppose to get 4 and 4.

what is the conclusion?


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