Affects Version/s: Minecraft 1.13, Minecraft 1.13.1
Fix Version/s: None
A nether portal don't light up when I activate a dispenser which is not against the side or the bottom obsidian. It work when you have a flammable block next to it (as shown in the seconde screen).
Same for the flint and steel, it work when you're next to the obsidian (not the top one) with all blocks but in the middle it do not light up the portal if it's not a flammable block.
Although it work with the fire-charge on all blocks. You can't use a fire-charges in a dispenser, obviously, becauseit shoot it ! (it's entended, i know)
What expected :
In all the previous versions it worked in all position, and all the blocks whether you use a dispenser, or the flint and steel directly with the hand.
Consecutive to :
In the 1.13 update the ability to create a flame with a flint and steel on all blocks even if there is no block bellow was remove.
This explains why you can't light up the portal with a flint and steel and when it's not against the obsidian, because you can't activate the flint and steel.
This do not explains why you can create a flame on a none flammable block when it's next to to the obsidian inside the portal frame (don't create a flame when it's not inside).