Start the Emacs hello file with C-h h.  Move the cursor on the
right-to-left mark in the Arabic line (it is enclosed by two parens, the
known compositing bug).  Press C-l for recentering.  Sometimes the
following line (Bengali) is mangled into the Arabic line.  It is not
clear to me when this happens: it apparently depends on the window
size/the current window contents non-locally.  I include a screenshot of
when this happens.