I recently switched my home planner to (setq planner-use-day-pages nil) and discovered that when I use remember and try to list multiple pages to link to, that remember seems to add that note to what ever page was listed in the minibuffer.

So, for example, if I got the prompt:

Page: (default: MainPage)

And I just hit RET, then the note goes to MainPage.
If I enter:

FooBar

The note gets entered only on page FooBar, and if FooBar doesn't
exist, it gets created.

If I enter:

Foo Bar

Meaning I want this note on both the pages Foo and Bar, then I get a new page created called 'Foo Bar'.

At first I thought it was because I wasn't using good WikiNames, but then I tried saving something to both 'MainPage' and 'GoodBeer', and that resulted in the buffer 'MainPage GoodBeer'.

I've checked that planner-multi-separator is set to space.

Also, if I take the default of MainPage, then use planner-multi-xref-note, it does the same thing if I specify multiple pages in the minibuffer. But if I invoke p-m-x-n mulitple times with a different name each time, it does the right thing (if you can call doing that "the right thing" :)