The task "ABC" with actuals 10 will still exist, but a new phase "~dtp" is created in the project hierarchy (appended to the bottom, typically), and the task will appear to have been moved under this. So "~dtp" is a new phase level record, and the "ABC" task and its actuals are still in the project, just moved from their prior position to being a child record of this new phase instead.
Example:
P1
- A2
- - ABC (actuals=10)
- - DEF
Upon deleting ABC and saving:
P1
- A2
- - DEF
~dtp
- - ABC (actuals=10)