I had a similar problem when I exploded Bentley elements. It turned out the elements' UCS was not 0,0,0 - maybe there's a similar issue here?
Type (assoc 11 (entget (car (entsel)))) in the VLIDE and select one of the offending MTEXTs prior to exploding it. Does it return, (11 1.0 0.0 0.0)? If not then that's your problem; if it does then it's still your problem as I haven't a scooby!