I've been using painter since 2006 and have always had a problem with large scale transformations.
Today I believe I've spotted why it so often freezes for me when transforming multiple layers on large format artwork and how to avoid it.
The key is in making sure the "shift" key is released before committing the transformation.
3.5Ghz 8 core with 16GB ram. Image is 420mm square at 600ppi.
Two small Jpgs are imported into the image as reference, made semi transparent to compare against the existing artwork and free transformed, stretching both layers simultaneously to about 1500% while holding down the shift key to maintain correct aspect. The tick is given to begin the transformation.
The notice comes up to say it's committing the transformation, but no green shows up on the progress bar. It's frozen at that point and goes no further. It's always done that on various machines and every version I've used since Painter IX.
The reason I continued to hold "Shift" while clicking on the tick to commit transform was to ensure the correct aspect was still held.
On very large transformations the preview often takes a few redraws before the final size shows up, release it before completion and the picture often distorts.
HOWEVER, continuing to hold shift after the preview has finished drawing to its final size and while clicking the "Tick" to transform.... will cause painter to freeze.
I wouldn't say that's a bug, but it's certainly a good thing to avoid doing:
Don't hold down shift while committing large transformations.