I compared my HTML source with yours, and noticed that mine contains some extra space characters. Not sure if that matters or not, but here they are, represented by underline characters for ease of viewing:
- &__amp;t=h
- &a__mp;ll=38.1 . . .
- &ou__tput=embed" . . .
- &__amp;t=h
- &so__urce=embed" . . .
The URL source from Google didn't contain any of these extra space characters.
On another note, would you mind sharing how you acquired the URL from Google? Did you use the "My Maps" feature? And do just plain driving directions embedd a map, too? Or a whole webpage as it does for me?
Thanks!