Basically what happened is vectric made changes to their grbl post processors. The changes were untested. The main issue is that they added arc commands (G2 and G3), but the calculations were not precise enough for GRBL’s checks. You’ll see errors more frequently if you use inches for post processing. Your design can be in mm or inches and you can still use either post processor.
The X-carve post processor, while grbl based, never included arc commands because Easel can’t handle them (weird). So, not only did they jack up the grbl arcs, but they passed that on to any grbl based post processor.
A while back, I had a desire to output a single file with multiple tools. I use CNCjs and have toolchange macros, so I am prompted for tool changes and the machine automatically adjusts the zero based on that new tools length. Anyway, when I modified the post processors, I added back arcs. Many others use my modified post processors and vectric was sending them to individuals looking to add tool changes. Soon enough, it was reported to me that some cases were causing arc issues. I fixed the arc precision issues (easy to change), so they don’t happen again.
Looks to me like a vocal grbl user had a specific need for some changes and they just change the posts.
On another forum, where people use my post processor for tool changes, it was reported that they still worked without issue with the new versions of V-carve and aspire.