This has happened several times now in a couple different assemblies.
I'll create a bolted connection. Lets say...with washers and nut it gives me a 2.75"L bolt. The engagement is just poking out of the end...but it's close enough so I move on.
I work on other parts of the assembly entirely unrelated to this connection, maybe open or save once or twice moving between different sub assemblies.
All of the sudden the bolted connection has the little update lightning bolt next to it. I right click and hit edit with design excelerator and every time it's already got the bolt showing as longer in the pane at the right. All I have to do is hit OK...I don't even have to touch anything else and it reloads the connection with that longer bolt.
Why is it doing this? Sometimes I've had it actually need another update later and it goes back to the original size.
Inventor thinks a change is being made somewere that affects the BC. It's a constant pain but RMB on the BC, select Component and then Solve Off. This will prevent it from automatic updates and prompting (the red lightning bolt).
It's simply the way the software is built. No point arguing with it, it's a feature that some like and others dont.
The best way to avoid this is to turn off the Solve OR place the bolt/washer/nut as individual items. Both have pro's and cons. Solve off stops the need to update but you must remember to edit the BC if you change the material thickness the BC penetrates. I'll leave it to you to contemplate what consequences placing the fasteners as separate parts creates.