If Broodmother levels up web while invisible on a web, she will become un-invisible as if she stepped off the web.
1) Stand on Web while invis
2) Level up web
Broodmother becomes visible to enemy units
Broodmother remains invisible as she has not left her web.
I believe this is an issue with her losing effects instantly when leaving the web, as I believe it replaces all webs on map with a higher level web when she levels it up. This was not an issue in past versions as she did not lose invisibility instantly.