I added some values to the custom columns on a single
task in a new project (Not yet saved) and these custom
columns and their associated values showed up in all of
the tasks that exited in the project at the time the
custom columns were added.
All tasks added after the custom columns were added
also contained the custom column data.
Logged In: YES
user_id=162766
Perhaps you specified a default value? If yes then behavior
is correct: all tasks which have no value in this column
automatically get default value