I would like to report an instance when R was forced closed without an error message.
I was running an ACE model with the components A C and E being matrices. When specifying the DZ twin covariance I used 0.5*A+C instead of 0.5%x%A+C, which caused the crash. Replacing the * by %x% fixed the problem.
Aside from the crash, it is quite tricky that * cannot be used for scalar-matrix multiplication, which is not consistent with R operations. To represent the scalar multiplication in a linear space as a special case of Kronecker product is a bit weird.