I am finding an issue quite intriguing in gimp.
I have seen several videos where someone just copies a part of an image in gimp, pastes it in and the starts to modify it whiles it is still in floating selection in the layer panel.
For example use the eraser tool on that paste in floating selection.

I cannot seem to do this. My eraser just cant seem to work in this layer mode unless i change it to new layer.

What gives? Am I missing something?

Just tried it - opened 2 images. added a new layer to one and copy pasted the other onto it. Applied eraser while the marching ants were still around the paste and it worked. A new technique for me and it might be usefull!
EDIT - just tried it without creating the new layer first and it still works.

Just now I checked and had no trouble with the eraser tool on a floating selection. What GIMP version are you using?

Cool - there is an antieraser too so you can finetune. But really just the same as using a layer mask isn't it. (and limited ie can't do a gradient)

At this moment I am running an unstable development version 2.9.9. This has been installed in the past 2 months.
But when I had 2.8 it was still the same issue.
I have also found some weird behavior that did not make sense. Difficult to remember, but I posted the question on Google gimp group.
Most could not understand what the issue was.

Could this be an interface problem. I have been running openbox as my interface for a long time now. Could this be the problem??

Thanks for checking. This is so strange.

I have got 2.99 on a new Ubuntu 1710 build and that is like you describe so maybe it is just a bug. But strange it didn't work for you on 2.8.

I have tried everything I can think off. Nothing seems to work.
In the layers panel I can seem to select the layer below. Are you all able to do that.
What I find interesting also is that a tool like perspective will work but not eraser.

Doesn't seem to work for me either; GIMP 2.9.9 on Kubuntu 16.04. The other tools work, but the eraser doesn't work unless I anchor the selection or paste it as a new layer.