A change that prevents transfer categories from being rolled-up into non-transfer categories, and vice versa, has been released for the Income and Expense and Budget pages.
As transfer categories fundamentally differ from non-transfer categories, rolling one into the other leads to a number of quirks, such as the income part of a transfer being seen as a refund when rolled up into an expense category, and other various nonsense.
You can find the full explanation of this behaviour on the Learn Center.
