I just noticed something weird in a site I'm working on. The first account is user/1 as usual. A second account I created two weeks later is user/20, and a third one a couple days later is user/32. Etc. Two accounts I just created right after each other are numbered consecutively as expected.
There are no custom modules modifying the registration process or anything. I wonder what could cause this, and if there's something I need to fix.