It is not nearly so simple.
Let us do some basic testing. I'm using v32 since that's what I happened to open (and OP is presumably using a fairly new version, since versions prior to the interface update wouldn't have tags, xref, and ladder in the same set of tabs).
I open the controller tags and a cross-reference, then a routine... each one is added to the right, exactly as one might expect. I then open a few more routines... again, each one pops up to the right.
It's once the space for tabs to appear is full that things get interesting. At this point, when I open a new routine, it appears to the left, as OP complained.
But wait! If I then open another new routine, it appears to the left... but the previous one vanishes. There's still only one tab to the left of the tags. What happened to the previous one?
Well, let's start closing routines and see where it shows up. I close the routine to the right of the xref tab, then repeat until I can see the routine in question come into view on the right. And one more closed routine later, the most-recently-opened routine, which had been sitting to the left of the tags, vanishes from there and appears on the far right. So these routines were in fact on the right, as one would expect from newly opened stuff.
...
At this point there's enough information to figure out some of what's actually happening.
The basic rule is not 'new routines open on the left'. It's something more like 'If there's enough tabs open that the current tab isn't visible, show it as the left-most tab regardless of its actual position,' and, since a newly opened routine becomes the current tab when you open it, as soon as you have enough stuff open it will always show up on the left side even though its actual position is far right past where you can see.
I can get multiple tabs to appear to the left of my actual left-most tab (the tags) by swapping between multiple tabs that are too far right to appear, but every time I open a new routine it consistently updates to have only the new, now-current tab showing on the left.
I suspect this is Rockwell's 'fix' for the fact that, in the new interface, you can no longer scroll right & left along your open routines. They needed a new way to show the selected tab if it isn't among the first [however many fit on your screen] opened, and this is it.
I'll be honest, I'm not particularly a fan of this behaviour. But trivializing it as just opening to the left isn't all that accurate.
