This wiki description sounds like it could be the behaviour Mojang intended:
"strongholds has increased to 128 per world. They generate in rings with the strongholds evenly spaced around the circle until the total of 128 is reached"
I see the algorithm was tweeked between 15w31c and 15w44b, but the current implementation has some issues that probably weren't intended. Which each new Stronghold, it's angular position is determined like this:
angle += 2π * ringNumber / structuresPerRing;
Which means everything works normally on the first ring (ringNumber starts at 1), but on the second ring it goes around the circle twice, placing two strongholds at the same position on the circle, on the third ring it places 3 strongholds together, etc. Due to the way distance is randomised, these stronghold clumps tend to be arrange in lines.
Diagram of stronghold positions for seed 2
You can see this is probably not what Mojang intended, except for ring 3, which probably is what Mojang intended, and works because the ringNumber (3) didn't divide evenly into the number of structures for that ring (13), so they didn't end up overlapping. The number of structures per ring is slightly randomised, so for the seed 2 diagram above, ring 1 has 3 structures, ring 2 has 6 structures, 3 has 13 structures and 4 has 28 structures.
If going around the circle more than once is intended behaviour, Mojang might not have noticed that ring numbers frequently divide evenly into structuresPerRing - random bad luck might have meant the seeds they tested on produced the correct behavior.
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I would say the 'buggy' behaviour is the clumps of strongholds generating. This is as opposed to speculation over what algorithm Mojang 'intended'.
yeah, "angle += 2π / structuresPerRing
" would give the behavior described by the wiki, but I don't know if that's what Mojang were intending.

I was looking for where someone already posted the strongholds not generating as intended. Still present in 16w02a. (edited to remove redundancy 😛)

Still present in 16w05b.
Easiest way to verify:
Run Minecraft, create new world (Creative), switch to Spectator mode
Run Amidst (v4 beta6), load newly created world, locate strongholds beyond ring 1 (get coords, 2 very close strongholds is best)
In Minecraft, tp to coords and look for strongholds (end portal room is best to locate as 1 per stronghold)
Note: while you may be able to load Amidst with the latest snapshot, for what I can tell, it currently can't recognize any snapshot past 16w02a, thus requiring visual verification.
edit: after looking through Amidst some more, it's not every ring, and it's not even the same rings every time; it varies per seed. Either way, adding a screenshot now.
I see two end portals in the screenshot.
Yes, that is the bug
You was so clever..
If I'm understanding this right, the formula should be changed to