The following thirteen(!) users: 

<a href="https://mathoverflow.net/questions/330472/functors-reflecting-colimits">goingfullscheme</a>  
<a href="https://mathoverflow.net/questions/330404/when-are-valuative-criteria-useful">valua_aint_no_galois</a>  
<a href="https://mathoverflow.net/questions/330390/schemes-admitting-a-cover-by-isomorphic-affine-opens">going-full-isomorphic</a>  
<a href="https://mathoverflow.net/questions/330342/connected-components-of-open-dense-subspace">logicians_rule</a>,  
<a href="https://mathoverflow.net/questions/330215/reading-off-the-geometric-properties-of-a-proper-scheme-from-its-affinization">martintzar</a>   
<a href="https://mathoverflow.net/questions/330207/are-geometric-conditions-open">royalroadtogeometry</a>   
<a href="https://mathoverflow.net/questions/330178/a-slightly-canonical-way-to-associate-a-scheme-to-a-noetherian-spectral-space">bundlist</a>   
<a href="https://mathoverflow.net/questions/330168/compact-quasi-coherent-sheaves">compactbut</a>   
<a href="https://mathoverflow.net/questions/330159/noetherian-stalks-imply-locally-noetherian">faptoint</a>  
<a href="https://mathoverflow.net/questions/330000/finite-picard-group">you_dont_mess_with_ron</a>  
<a href="https://mathoverflow.net/questions/329997/affine-open-with-irreducible-complement">ron_is_striking_back</a>  
<a href="https://mathoverflow.net/questions/330453/algebras-such-that-the-tensor-product-with-any-noetherian-algebra-is-noetherian">Emmy_to_Noether</a>   
<a href="https://mathoverflow.net/questions/330337/noetherian-and-finitely-generated-for-polynomial-algebras">commutative_drinker</a> 

(and, I believe, a couple more besides) have the following characteristics in common:

<ul>
<li>They've all joined in the past few days.</li>
<li>Each has asked exactly one question</li>
<li>Their questions are closely related to each other</li>
<li>Their writing styles are very similar</li>
<li>After posting their questions, they never return to engage with commenters, or to acknowledge answers</li>
</ul>

I think it is not too much of a leap to conjecture that these are all the same person.  

As far as I know, there's no actual rule against having fifteen different identities (or for that matter, a hundred, as seems likely if this keeps up at this rate for a few more weeks), and no actual rule against asking questions and then systematically ignoring responses, but I still find it troubling in ways that might or might not be entirely rational on my part.  Do others share my discomfort?

<hr>
Edit (YCor June 3, 2019): since the question was posted, here are a number of similar posts:

[user138661](https://mathoverflow.net/questions/330690/grothendieck-topology-on-a-scheme-equivalent-to-the-circle) (account closed since then: not the original post name)<br>
[m_for_motive](https://mathoverflow.net/questions/330766/proper-variety-containing-no-affine-open-with-irreducible-complement)<br>
[drama_dorama](https://mathoverflow.net/questions/331666/the-underlying-space-of-an-affine-open-dense-subscheme)<br>
[gentleman_gaga](https://mathoverflow.net/questions/331914/does-the-structure-morphism-matter-in-gaga)<br>
[motive_for_m](https://mathoverflow.net/questions/332103/a-different-sort-of-affinization)<br>
[livehard](https://mathoverflow.net/questions/332120/equipotent-non-homeomorphic-schemes)<br>
[user141225](https://mathoverflow.net/questions/332839/checking-universal-closedness-on-immersions)<br>
[PDShoot](https://mathoverflow.net/questions/332949/scheme-locally-of-finite-type-over-the-affinization)<br>
[Gimme An Answer](https://mathoverflow.net/questions/332951/the-ring-of-global-sections-of-a-regular-scheme)<br>
[La fille](https://mathoverflow.net/questions/332969/non-empty-affine-open-with-an-irreducible-complement)<br>
[Name](https://mathoverflow.net/questions/333039/strongly-abnormal-schemes)<br>
[Name](https://mathoverflow.net/questions/333008/quasi-compact-morphisms-satisfying-the-valuative-criterion-of-properness) (not the same as previous one)<br>

(there are a few more, for which the similarity is less obvious). In addition, this June 3, 4 of these posts have been bountied by other users: [cardinal](https://mathoverflow.net/questions/332103/a-different-sort-of-affinization), [Cut the wood](https://mathoverflow.net/questions/332969/non-empty-affine-open-with-an-irreducible-complement), kartop_man ([this one](https://mathoverflow.net/questions/332949/scheme-locally-of-finite-type-over-the-affinization) and [this one](https://mathoverflow.net/questions/332969/non-empty-affine-open-with-an-irreducible-complement)). 

--- 

**Edit:** I'll add more as I see them. Please note that these accounts have a tendency to comment on, edit, and answer each other's questions. The situation is similar to that of another user and his ring of accounts a few years ago that some of you may recall, and who is now permanently banned from SE. 

https://mathoverflow.net/users/141417/etalien 

https://mathoverflow.net/users/141410/topo-mopo