You can amend rules so your Sage HR knows what to do when a shift is added that clashes with an existing time off request.
Only users with admin or scheduling admin access can follow these steps.
Click your name in the top right, then click Settings.
On the settings menu click Scheduling, then click General.
Scroll down to Rules when adding shifts.
Next to each of your time off policies, select whether to allow or not allow the shift to be added when a shift manager adds shifts when there is a time off request on that date.
Scroll down and click Save.