In the case of Fidelity, they don't show the transfers in and out of the core account. That's just fine with me. The core account values are simply shown as cash in the account in Quicken. I know that this amount is actually invested in a core MMF, but I don't need to show it as a security owned in Quicken. Having it shown as cash value is fine, and reduces the number of transactions in the register. Since the share price of the core account is always $1, then $1 cash always equals 1 share of the MMF. I will say, however, that I do occasionally receive a random buy or sell of the core account. Just once in a blue moon. Not sure why this happens, but I just delete those transactions when they do download.
Even though I, technically, hold a cash position in a MMF in several of my accounts ... I have never understood the benefit of recording the security transactions in and out of such MMF.Instead, I just reflect the cash as cash ... and everything works just fine.