iTunes: Copying album to iPhone interrupts copy in progress

I'm not syncing: I'm using "manually manage music"

I used to be able to drag an album onto my phone, switch to another artist, drag the second artist's album onto the phone, and it would then queue the second artist's songs onto the list of files to be copied. I could continue to do this, dragging various albums over and over until I had a large queue of songs which would eventually complete copying.

Now, if a copy is in progress and I try to add another album, the album copy in progress is interrupted and I see a "grayed out" listing of songs on the device (the songs are not there).

What's going on ??

I spent some time with Apple support, and even went as far as doing a screen share so they could observe my iTunes in action. They also tried it on their side and basically confirmed that this is just the way iTunes works now.

If you "manually manage" you must let each transfer complete before initiating another.

I suppose you could create a giant playlist and just sync that, but I prefer to manually control everything. This is not a big issue once you've filled up your new phone and only need the occasional transfer.