The previous comment may be correct in that much lower than nominal currents tend to numerically ring in a simulator, particularly when zoomed in on a graph.
Conservative mode usually solves this in spectre, but you may need to tweak the analog options too.
Or it could be once you combined things, you unwittingly share a net name, such as a bias.
![Wink Wink](https://designers-guide.org/forum/Templates/Forum/default/wink.gif)
As you say, ideal supplies should be fine.
~WAVE