If a user changes the item type for a given item key to an incorrect one and then changes the item key to a custom key, the item type warning icon is not removed.

Steps to reproduce:

1. Open item configuration form
2. Enter agent.hostname in Key field - observe that Type of information was changed to Character
3. Change Type of information to "Numeric (float)" - observe that a warning icon has appeared next to the Type of information field
4. Change item key to some custom value, like agent.salary

Result: the warning icon is still there, even though a custom item key is used (which is not assotiated to any Type of information value)
Expected: Since a non-pre-defined item key is used the Warning icon should not be shown.

Example: