I have been using omnipod for just over 2 years and the description you gave has described exactly what has happened to me on a couple of occasions.
my BG's are normally between 4.8 - 6.5 when I change a pod and I have experienced a slight rise over the first 3-4 hours even with no eating ( to between 8.0-9.6 ) , but it settles down within 5-6 hours
however on a couple of pod changes my bloods started rising relatively quickly and within 3 or 4 hours were touching between 14 - 18 , despite corrections-- on these occasions I just changed the pod and was soon back to mid single figures ( 5.0 - 7.0 )