I ran into an issue where when I copied SVGs from one Inkscape file into another one, the result was the SVG was converted to a bitmap.
My post was here: Bug in UI? Multiple Items
After some Googling, I found this to be an issue in Inkscape on the Mac.
Here is how you fix it:
Disable ‘Sync PasteBoard’ functionality within the XQuartz app to solve the problem of converting a vector object to Bitmap after pasting the same object in another SVG file.
On the Mac: XQuartz (X11) > Click on ‘Preferences’ tab > Choose ‘Pasteboard’ tab > Uncheck ‘Enable Syncing’
Once you change that setting copy/paste should work correctly!!