You cannot light more that four nether portals directly next to each other

Put the summary of the bug you're having here

What I expected to happen was...:
I thought I could place more that four nether portals next to each other (purple swirly stuff facing eachother)

What actually happened was...:
Once the fourth portal was lit any more would just have fire and not ignite into a portal

Steps to Reproduce:
1. Place one portal and light

2. Place another portal so it is flush with the other (purple portal blocks facing eachother no seperation)

3. Place another portal in this same order and light

4. Place another portal in this same order and light

5. Place another portal in this same order and light, but the purple blocks will not come and it wont be functional