Problems with issymmetric and sparse matrix

I have a real sparse matrix, say A, of size 21660x21660. Here are my observations:

 1. Running 0==max(max(abs(A-A'))) returns 1, so I could say that A is symmetric.
 2. When I run issymmetric(A), it fails returning 0. 
 3. Trying issymmetric(A+A') also fails returning 0.
 4. Trying issymmetric(full(A)) also fails returning 0.
 5. The previous did not fail with a random symmetric sparse matrix of the same size.

I'm shocked by number 3. Any thoughts? I'm using version 2016a.

[Ivan Gonzalez Bustos]

Sorry! uh... found some NaNs in my matrix! I'm going to leave this here in case someone is as stupid as I am.