rhuxds

Thanks you so much! Also glad Google indexed your answer high up.
I do get where the person is coming from you gave this answer to. I bought Affinity about a year ago, and from having used Photoshop for many years but refused to pay subscription fees, I just assumed that most of the operations would more or less follow the same paradigm, since i presume photoshop users are part of affinity's core target market, but maybe not... Anyway, not bitchin, but seriously  almost every operation I take a shot at using just by guessing based on tool icons and tool tip descriptions, 9 time out of 10 there's a different operational paradigm and i just don't get it. What you say makes sense re images being considered an object that must be rasterized... and maybe somehow photoshop would handle that automatically when i drag and drop objects onto the image area to create layers. What's impt is now i know, but i cant tell you how many videos i started to watch in Youtube about background removal using flood tool, only to follow their directions but after selecting,  and what appears to be an intelligent selection based on pixel color, hitting delete thinking the selection will be deleted only to find the whole layer deleted. 
it just never occurred to me that i'd have to take an action on an image beforehand...  Really appreciate your quick to the point answer which was the secret sauce! thank you much!

I'm glad I found this thread, it looks like an software wierdism. I had four layers, one where i selected an open Affinity image and two where I dragged them in from explorer, plus the origibal image.
The pasted image behaved as expected but the two dragged layers just got deleted rather than the selection. All were pixel images, so I cannot see why the problem exists but MEB's response works perfectly.
There are some wierd aspects to Photo but c'est la vie.
The problem is, really, that the image layer is an undocumented feature.

I'm sorry I do not get why you are telling all this stuff about where selection belongs to. What does it matter? Selection is still a vector (a geometric, connected shape defined by X.Y coordinates of its points), and in its nature it cannot have overlapping areas of its own parts. Which makes it simple and perfectly suitable for implementing the requested delete feature by applying the exact same modifications as the "Image layer" has, and deleting the pixels in the original bitmap even though the original bitmap is contained inside a scaled and skewed "Image layer". I'm willing to bet two beers that once I got familiar with the codebase of Affinity I could code such operation in a day. This is not what I call hard to build.

Thanks. I got that from the previous posts in this thread. The functionality is a useful addition, which allows out of the box image manipulation without losing the resolution and revert changes.

I also understand that current versions of Affinity Designer/Photo are unable to delete bitmap pixels form a selection on top of an Image layer.

From my perspective it should be possible to implement ('walking ants' selection path is a single vector path anyway, so just apply size/scale/skew from the image layer in reverse order to the underlying original bitmap and delete those pixels. voila). This should be applicable to Erase Brush tool just as easy. Please put this on your roadmap. You know people want it.