You can't move them past one another but other than that they should move but sometimes hit an invisible wall.
Are you aware of the different moving options too? If you click on the diamond and move it, the audio marker moves position relative to the audio (ie if it 'guessed' the transient incorrectly - you correct it) but if you click the vertical line and drag it, you can manually quantitate that node.
My gut feeling is its not a bug, but you just need to get a feel for how it all works. It can be a little tricky at first. Some folks here I think simply refuse to use it because it just never makes sense to how they like to work. I personally think its great and don't have any major concerns with it at all. You just need to learn it and understand its limitations. Like pitch correction, your safest bet is to always do plenty of manual work. It's time consuming, but you can't always trust auto. To clarify, I use the quantitate feature, but always pre check my nodes (that they got the transient right) and post check that it quantized properly.
Give it time and you'll master it