why does this use LMMathItalic10-Regular for the OS numbering?

\startitemize[m,packed,text]
\item a
\item b
\stopitemize

\os clearly works in other parts because it's using minion

% pdffonts file.pdf
name                                 type              emb sub uni object ID
------------------------------------ ----------------- --- --- --- ---------
TCLXBY+MinionPro-Capt-Identity-H     CID Type 0C       yes yes yes      5  0
JAHMWQ+MinionPro-Regular-Identity-H  CID Type 0C       yes yes yes      7  0
UGISSP+MinionPro-SemiboldDisp-Identity-H CID Type 0C       yes yes yes
 9  0
LBRKWQ+MinionPro-SemiboldSubh-Identity-H CID Type 0C       yes yes yes
13  0
*FVROKN+LMMathItalic10-Regular        Type 1C           yes yes yes     14
 0*
VQGIRJ+MinionPro-Semibold-Identity-H CID Type 0C       yes yes yes     16  0
TMNGMR+MinionPro-It-Identity-H       CID Type 0C       yes yes yes     18  0

% pdfinfo file.pdf
Title:          x
Subject:        x
Author:         x
Creator:        ConTeXt - 2008.05.21 15:21
Producer:       xdvipdfmx (0.7.3)
CreationDate:   Sun Jan 24 17:11:23 2010
ModDate:        Sun Jan 24 00:00:00 2010
Tagged:         no
Pages:          2
Encrypted:      no
Page size:      595.28 x 841.89 pts (A4)
File size:      39591 bytes
Optimized:      no
PDF version:    1.5


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—Mohamed