Cactus spawning next to blocks

What is the level seed + the coordinates of this?

ive noticed this too it occours when the world is generated and does not "check" for glitches this is also apparent in things such as torches in mineshafts (not lighting properly) and things like that maybe if the world did check when generating this could be fixed

Not so much a bug as a feature of the world generator.

I would say failing to check/maintain surrounding blocks when generating the world can be considered a bug...
At least, resolution would be "works as intended" if that is indeed the case, rather than "invalid".
All the strange "features" of the world generation, like this, could be fixed, but maybe not worth it...
But it can be cool to find strange things like this in the world, so would make the world less interesting if the generation was made "sane".

Most likely placed by an Enderman MC-5860

Cacti themselves cannot generate next to solid blocks, the problem is rather that other structures can generate next to cacti, but that is indeed likely intended.