Not sure if you visit here or not anymore but if you do and see this -
I just had v3.5.1 installed last night (w/new nav card). On my drive to work this morning I was digging through some Nav settings and came across breadcrumbs and it reminded me of your question. For the hell of it I turned them on. It laid them down for the remainder of my drive to work (about 10 miles). When I left work, they were still there and it continued to put new ones down as I backtracked that 10 miles. After I got to that point it still continued to put them down, all the way to my son's Tae Kwon Do class. When we left Tae Kwon Do, I was able to backtrack as they were still there until I veered off towards my house. They continued to be put down on the new roads. So far it looks like about 40 miles of driving and they are still everywhere I drove.
Going to leave them on for a couple of days just to test further but in a nutshell it appears that v3.5.1 may have fixed the issue.
.......here's a lockpick. It might come in handy if you, the master of unlocking, take it with you.