interesting. today when i preview, the new params are there in vs. i have to conclude that the act of deploying these reports updated something on tfs, perhaps because a build always happens with a deploy.
but on a related note, and specifically in regards to another post i have where a multi value param is being ignored (maybe cut off) in a sub report, i posted there an xml reference to ssrs 2008 in the sub report. whereas the parent's xml shows 2016. so i deleted that subreport after reading your answer here, redeployed it and made sure it was rendered. ssrs didnt upgrade the version. so that remains a mystery. i haveng looked today to see if there are any answers there at the other post yet.