font behavior

I’m experiencing odd font behavior in one particular document within DTP:
I can paste text in, in a font other than the one used in the rest of the doc. It appears in the desired font if I paste it into the doc when the doc is viewed in the pane under the list view. But then if I double-click on the doc to open it fully, the text in the new font is transformed to the doc’s overall font. Say I paste this in:
㊥ hiragano mincho ProN

It includes a glyph unique to hiragano, plus some ordinary text. It all appears in Hiragano. When I double-click the doc in the list it opens and all text is in Georgia, my usual typeface. But viewing the doc in the pane, the Hiragano remains Hiragano still.

Also, if I select a word in the doc while viewing it in the pane and change its font (using Command-T to bring up the font chooser) then everything in the doc changes to that.

Is this some malfunction in my system, a corrupted document, or ???

Cancel this, the behavior is more complicated than I described. And not all my description is correct. I need to explore it some more. Sorry.