Is there anywhere in WP that a username/password may persist after deletion from WP Users table?

In my non-Multi, non-Buddypress WP site I have several usernames that I would like to reuse. These were usernames that previously existed but have since been deleted from the WP Users table.

However, I get the feeling that even though these accounts have been deleted (and I confirmed that they do not show up in the Dashboard "Users list" nor in a phpmyadmin display of that table) I feel that there is some residual trace that still exists somewhere.

For example, say that "1234 /password" was a Users table entry that previously existed but has now been deleted. However, although "1234" no longer exists in the Users table when I nevertheless attempt to login with "1234" I get different results depending on whether I try the original password or another value.

(And to repeat: user "1234" no longer exists in the WP Users table, so I should consistently be getting the standard WP "invalid username" message regardless of whether I use the original password or not)

Scenario A: I try to login with "1234 / password" (i.e, the original username and the original password - both of which were deleted when that WP Users entry was previously deleted): the response is a browser-generated error message "No data received" (which is a Chrome-based browser error message; note that I get differently-worded but similar browser-based error messages when I try different browser types - such as "The connection was reset - The connection to the server was reset while the page was loading." that I get when using Firefox).

Scenario B: I try to login with "1234 / notpassword" (i.e, the original username but a password different than the original password - but of course it should not matter because "1234" has long-since been deleted): the response is the standard WP error message that I would expect to get... "Invalid username".

So, why does Scenario A give me a different response? It acts as if there is some trace somewhere of the long-deleted "1234 / password" account.

Note also that I have tried clearing browser cache and cookies, and I have tried different browser types on different computers as well as browsers on different networks and I always get the same discrepancy between Scenario A and B.

So, somewhere there is some retention of the old "1234 / password" combo other than in WP User table and other than cookies and browser cache. Do you know where that is? (and no, I am not using a WP cache plugin, and yes I did try other themes including Twenty Fourteen and got the same results).

Thanks in advance