How are you trying to update the grid with JS?
I took a quick look at it, but I couldn't figure out how to attach a server event to the grid's form. I guess it's the form Core_ItemGridLayout that renders the grid, but I might be wrong. Since no form is specified in the Part ItemType's TOC View relationship, or in our custom Part ItemType for that matter, I assume it automatically falls back on the standard grid. But maybe it's overkill to try to override the default grid.
Perhaps it's possible to add a JS method under the ItemType's Server Events or Client Events that gets called whenever the item is saved. I guess you could escape the item's tab by using parent in JS and then locate the grid iframe which seems to be named work, i.e. parent.document.getElementById('work').
