The following code fails; however, it succeeds without newotf, and it 
succeeds with newotf if the defined font feature (*hebrew) is removed 
from the \definefont command. The characters that demonstrate the 
problem are HEBREW LETTER LAMED combined with HEBREW POINT HOLAM, 
followed by HEBREW LETTER ALEF (U05DC with combining U05B9 followed by 
U05D0). I have not come across other combinations that cause the 
problem, but I have not done an exhaustive search.

    \usemodule         [newotf]
    \setupdirections   [bidi=global]
    \definefontfeature [hebrew] [default] [lang=heb,ccmp=yes,script=hebr]

    \definefont        [Hebrew] [sileot*hebrew]
    \starttext
       \startTEXpage
         This is okay:{\hfill\Hebrew לא}

         This is okay:{\hfill{\Hebrew לֹ}}

         This fails:{\hfill{\Hebrew לֹא}}
       \stopTEXpage
    \stoptext

It reports:

    error:
    C:/ConTeXt/tex/texmf-context/tex/context/base/font-ots.lua:1586:
    attempt to index a number value

    tex error       > tex error on line 13 in file
    C://Users/rik/Desktop/newotf-features.tex: ?

    <inserted text> \par

    <to be read again>
    \vss
    \pack_framed_do_bottom ...amedparameter \c!bottom
    \raggedbottomcommand
    <to be read again> \localendstrut \pack_framed_do_bottom
                                           \egroup
    \stopfittingpage ->\removeunwantedspaces \egroup
                                                      \egroup \doif
    {\fittingpage...
    l.13   \stopTEXpage

The same problem occurs in the same way with the following fonts, most 
of which are shipped with Windows:

    Arial Regular
    Arial Bold
    Arial Narrow
    David Regular
    David Bold
    Ezra SIL Regular
    Ezra SIL SR Regular
    Keter YG Medium
    Levenim MT Regular
    Levenim MT Bold
    Taamey David CLM
    Tahoma Regular
    Tahoma Bold
    Times New Roman Regular
    Times New Roman Bold