Without looking carefully at a specific case, I think its because of missing closing segments in some truetype character definitions as has been suggested above.
It’s legal to have a truetype font contour that’s not explicitly closed and the last segment is added when the charater is rendered.
The TextObject command deals with that pretty carefully. The checkbox about single stroke fonts disables adding the last segment so that special purpose fonts that meant to render as curves and not filled areas for machining, etc work as intended.
It looks like a bug in text explode that the closing segment isn’t added when it’s missing, but instead the last point of the last segment that is there is moved to the start of the contour.