All Transactions filtered view shows split total rather than selected category (Q Mac)

It's definitely a well-known issue. The developers would tell you it's not a bug, but working "as designed". In the way Quicken is currently built, any transaction register is only going to show transactions matching whatever criteria exist: which account, date range, other filters, or search text. It does not have a capability, or even a format, for displaying a register consisting of both regular transactions and pseudo-transactions representing split lines extracted from larger transactions. I'm sure there are ways it can be done, and it would be a useful enhancement, but it's just not built for that at this time.  

The splits part of the Quicken interface were originally built for the predecessor Quicken Essentials program a decade ago which served as the base for the modern Quicken Mac -- and haven't been worked on in any significant way since then. There are a number of other limitations with splits. If you select multiple transactions, you can mass edit them together -- but the mass edits, such as applying a category, don't work on split lines, only simple transactions. On the screen, the splits interface doesn't match the columns settings (which columns are shown, in what order, and how wide) a user has set up for the register. I hope the developers will at some point return to splits and modernize several of the aspects about how they work.

Meanwhile, is it possible you can accomplish what you want with a quick Report instead of register? If you go to Reports and select Transaction by Category, set the date range you want, click on the Categories tab and Clear All, then select the category(its) you want, the resulting report will list all the matching transactions -- and here, only matching splits will show, not entire transactions.