This normal and it always has been like this, GSX is not programmed to remove or send away a staircase it has already generated when the embedded airstair was still retracted.
Changing this would require GSX constantly monitoring at any time the airstairs since it should be ideally able to remove its stair at *any* time you extend it, possibly even when passengers are already using the GSX one (we can't possibly know when you'll extend it), so it's quite tricky and easily leading to issues.