attachMovie with jpeg from library CS4

Has attachMovie changed behaviour in the last 10 years?

I’m running the following code:

_root.createEmptyMovieClip("holder", 1);
_root.holder.attachMovie('p1','image_1',2);
trace(_root.holder.image_1._width);

Trace outputs 0 and no picture is displayed.

p1 is a jpeg placed in the library with the identifier p1 and ‘Export for as’ and ‘Export in 1st frame’ are checked.

If I place the jpeg in a symbol/mc and call it with attachMovie, the picture is displayed.

What’s going on?