[XeTeX] Fontspec v2.4 (25/05/2014) misbehaving?

[Elliott Roper]

A freshly installed TeXLive 2014 produces OK output from its version of fontspec’s fontspec-example.tex, but after updating with TeXLive utility the new one fails with
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ERROR: Undefined control sequence.

--- TeX said ---
\__fontspec_calc_scale:n ..._tmpb_dim }\fp_div:Nn 
                                                  \l__fontspec_tmpa_fp {\l__...
l.8 ...sfont{TeX Gyre Heros}[Scale=MatchLowercase]
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That is followed by
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ERROR: LaTeX error: "kernel/misused-fp"

--- TeX said ---
! 
! A floating point with value '4.490005493164062' was misused.
! 
! See the LaTeX3 documentation for further information.
! 
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It looks as though it has forgotten how to do floating divides.

Removing the options e.g. [Scale=MatchLowercase] allows it to compile a pdf but of course with ugly sizes.

Reinstalling a fresh 2014 over the top of it returns it to sanity but with options preceding the font name as in 2013.

This in on a Mac with 10.9.3

Elliott Roper