Priority is a very badly mis-named field.

In the actual world, these are two separate things:

Importancy - how important it is for this issue to be solved.
Urgency - how fast this issue must be solved.

Issues are rarely important & urgent. If you have 1000 clients and 1 client can't run your software at all and needs it for his mission-critical tasks, this is urgent, but (from your perspective) not very important.

On the other hand, a bug that is very severe but rarely encountered in daily use is very important but not very urgent.

Priority is, by this definition confusing. If priority is "Critical" does this represent an important or an urgent issue?

Therefore I suggest that you at least make it possible to use this feature either by:
1. moving to important/urgent model instead of priority
2. letting the user decide which model to use (either at install or being able to change it dinamically)
3. at least let the user hide/rename the "Priority" field to - for example - Urgency and add the Importance field.