Ben said this issue was more involved than expected. 

It is not something that has "regressed" from the previous release so I think I think we can postpone this fix.

I tried it on git da42f941ea2e14fe2 and I can confirm that it does not work.
The variable view shows the variables but the data view does not show the cases after copying.

Frans Howelling also reported this:

DATA LIST LIST /area (F1.0) price (F12.0).
BEGIN DATA
4    1805
1    1945
4    1412
END DATA.
DATASET COPY WORK_A.
DATASET ACTIVATE WORK_A.
AGGREGATE OUTFILE = * /BREAK = area /price = MEAN(price).
DATASET NAME OTHER_1.
DATASET DISPLAY.
DATASET ACTIVATE WORK_A.


In SPSS:
- after the DATASET COPY command I see 2 files: *Untitled[] (active)
and *Untitled[WORK_A]
- after next command (DATASET ACTIVATE) I see *Untitled[WORK_A] (active)
- after AGGREGATE I see *Untitled[WORK_A] and *Untitled[] (active)
- after DATASET NAME I see *Untitled[WORK_A] and *Untitled[OTHER_1] (active)
while PSPP has only 1 file left at this point.
I tried PSPPIRE to follow the steps, but it I guess it doesn't honor
the DATASET COPY command.