I've been amused by this bug ever since I discovered it last night. Its minor and visual only, but it does look pretty weird, so I thought I'd post about so it gets fixed very eventually

Build 2 frigate factories. Queue lots of HCs. Add another factory. When the original 2 fabs finish their current job, one of them will insta-switch to the HC the 3rd (new) fab was working on, and spit it out when its done, with the 3rd fab looking like its not doing anything (HC stays transparent), then when the HC the 3rd fab was originally working on is done, the 1st or 2nd fab spits it out, and goes back to doing what it should be doing, and so on.

If make a really long queue and keep adding fabs - with the right planet - you can get some pretty mesmerising ping-ponging of half-built ships between the factories, and they all still come out of the fabs you had at the start, no matter how many you added later