On master and 2.5 (please test on 2.4 too)
a) Fresh install
b) Admin > Appearance > Theme settings: enable allowcoursethemes and allowuserthemes
c) create a course, enrol yourself, in appearance force theme to Boxxie
d) Edit your profile and select MyMobile theme
e) Go to the front page, mymobile theme is well displayed.
f) Click on the course on the front page => a mix of clean theme + mymobile theme is displayed.
g) purge the cache, all is back to good.