ETA2, 6-14-17: Request filed.
ETA, next night: Definitely need to report or at least ask about this over in Support; I tested my page in Pingdom last night and both recent icons I used in posts came up with the same file number, again, which rules out my computer as the cause. Got a screencap of Pingdom reporting them as such.
In this delightful bug, if you go to the Upload icons page and right-click/Save Image As, any icon you choose saves with the same image name: 440557.png. I mean, they all do. This in Firefox latest on Windows 10; you're mileage may vary and if it does, I'd like it if you let me know (I do have other accounts I can test this in, which I have not done yet) before I file a support request, which is still a ways off.
Testing the Update page as I write this, if I click the icon next to my username in the upper right hand corner (using the default site skin, I think it's called Tropo) the file saves with the same name, 440557.png. So all the icon images have the same name. I mean, I *think* this counts as a bug, that all the icons have the same names/numbers, so I'm thinking of reporting it.
What I'm testing here is a different icon than my default to see if posts show different icons with the same image number as well (probably will; post Preview page shows the same image number on right-click/View Image); this post can also double as a reminder to report this, eventually.