Dispensers with Flint & Steels do not power a portal if its size is irregular

What I expected to happen was...:
Using a flint and steel in a dispenser toward a portal with an irregular (1.7+ only) size will activate the portal.

What actually happened was...:
After the puff of smoke nothing happened and the flint and steel durability didn't change.

Steps to Reproduce:
1. Make a portal with an irregular size, like 3*5.
2. Place a dispenser with a flint and steel towards it.
3. power the dispenser.