I'm glad I found this thread!
This issue is still there. I couldn't edit negative values for pitch wheel data because you can only see anything (for values below zero) if handles are enabled. Of course I couldn't enable handles - because as you know, I enabled them in the menu, bu tnothing happened!
FBB's fix is still appropriate - and although it's a nuisance, it works. Like some others, I don't normally like to see the handles on controller data - but for pitch wheel data, this is the only way you can edit them in the PRV. Above zero values (for pitch wheel) are normal, so this is doubly bizarre!
Anyway - thanks a lot fastbikerboy for discovering this obscure fix!