I have been looking at the JTech version of grbl and have noticed a potential problem for those that use that firmware.
The problem will only occur if you issue a command line change to the status report mask ($10). If you change the status report mask the firmware appears to also change the Junction Deviation value ($11).
Maybe someone with this firmware can test it to see if that really occurs (be sure to write down the value of the Junction Deviation so you can put it back if it gets changed).
I have sent a request to JTech customer support to see if they will also look into this issue.
Forgot to mention it’s version 0.9g J Tech build 2015124