Self-explanatory. One source block and one flowing block generate, but the rest doesn't.
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Unsure what you mean with this.
What did you do, what did you expect, what happened instead?

@Grum sorry for the ambiguity. just load up a world, set yourself to spectator mode, and fly around until you spot a water/lava spring in a ravine or something. The source block and first flowing block generate fine, but you need to manually update the flowing block for it to keep flowing downwards like it should. Also happens with some lava springs in the nether- rather than flow downwards towards the floor, the flowing lava block just sits there until updated.
I noticed this behavior too in 14w25b.
Reproducible. Created once more the same seed 2732436332148727145 and used teleport to the coordinates in the screenshot.
Still present in 14w26b.
My issue which was resolved for being a duplicate (which it isn't), is about the same snapshots, however it's everything, not just lava. When I place water, it flows extremely slowly, mobs are extremely slow, potions bounce off the ground and break 5 seconds later, other thrown entities do the same. I have a video on mine, MC-59097. Hope it gets fixed.
@Cosmicluck. I agree that is not a duplicate. Supposing that previous versions of the game were running fine (so you have a decent computer) then you should try to check the environment. Changing Java version, updating video drivers, changing settings in the game, lauching the game in another OS (linux), lauching it with a severs-client solution (both on your computer), checking free space on the hard drive... etc
The Mojang comment for 14w25b was "It is very likely that this snapshot may be more unstable than usual, slower than usual..."

Fixed?? Maybe?? I'm not really seeing this happen anymore, at least not enough that it would be a noticeable bug were 1.8 to be released right now. Since Mojang hasn't officially resolved it yet, though, I might as well update the "affected versions".
I can reproduce it with 14w27b. Not anymore with 14w28b and 14w29b.
In 14w28b I noticed something interesting: when I teleported to the 520 59 363 coordinates in 2732436332148727145 seed, the lava was already touching the floor and also was already spread one tile from the contact point. But it took a very long time until the lava has extended 2 more tiles. The feeling is like if the game is pre-calculating the liquid flow more steps in advance before it starts simulating the newly loaded chunks.
In 14w29b I did not noticed this problem but first time the wall textures were not loaded at all for 1-2 minutes (I could see through walls) but I could not fly through them.

I think you're describing two separate bugs, and I'd link them if I weren't too lazy to go and find the right ones. Basically, there's one where flowing water/lava doesn't visually appear for a couple of minutes, and I'm guessing you ran into this with the lava spring since it showed up fine for me. The second is where chunks themselves have this behavior, almost like every block in the chunk is turned into a barrier block, invisible yet present.
@clam lol. You are right, the lava starts to flow after a short time. Good remark.
((The game behavior must have changed now that you game me this knowledge 😃 ))
I tested again with 14w27b, 26c and 25b and in all cases after teleport to the location the lava started to flow after a short time (less than 2 minutes). When I noticed this behavior first time, I was exploring the area. Possibly the time to update can be longer when people play normally, exploring around. If is long enough, maybe it doesn't start at all.
Regarding the second problem I didn't even tried to report it. I mentioned it because it was preventing me to see the lava and its behavior 🙂

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.

Stumbled upon this old thing again- it was fixed even before 1.8.
EDIT: Necrobumping a topic causes a bot to reopen it. Whoops.
Fixed somewhere between 1.8.8 and 14w30b. Thank you for the response.