MantisHub team has just released MantisTouch v1.3.0 with custom fields support. The support for custom fields has been one of the most requested features, blocking some MantisBT instances from being able to leverage MantisTouch due to their reliance on custom fields in MantisBT.
This is now available to all MantisHub users with the appropriate plans as well as users that has purchased MantisTouch as a standalone offering.
MantisHub 