Never seen or heard of that as a problem: and SQL Identity fields are used so often I'm pretty sure it would show up.
Are you sure that is exactly what is happening? It would be easy to see that kind of change if rows are deleted for example, since the identity values will not be reused.
Insert 5 rows:
INSERT INTO MyTable (desc) VALUES ('One') ('Two') ('Three') ('Four') ('Five')
Gives you:
1 One
2 Two
3 Three
4 Four
5 Five
Then delete a couple:
DELETE FROM MyTable WHERE id IN (2, 4, 5)
And add a couple more:
INSERT INTO MyTable (desc) VALUES ('New') ('And again')
And you end up with:
1 One
3 Three
6 New
7 And again