wrong writingSystems determination for some 3rd party fonts

I have custom true type font, my company bought from 3rd company.
when enumerating with EnumFontFamiliesEx in qfontdatabase_win.cpp:populate_database, this font in qfontdatabase_win.cpp:storeFont function has script ="Cyrillic" and signature={fsUsb =

, fsCsb = {0x97,0x00}}, so this font contains Cyrillic symbols, but at the end of function qfontdatabase_win.cpp:addFontToDatabase value of family->writingSystems has set only byte correspoded to QFontDatabase::Symbol. So I can't use this font for Cyrillic symbols

As I can see in qfontdatabase_win.cpp:addFontToDatabase for True Type fonts function determineWritingSystemsFromTrueTypeBits is used, and no script check is occured, so script="Cyrillic" is ignored
Even More: in qfontdatabase.cpp:determineWritingSystemsFromTrueTypeBits function there is only check of signature->fsCsb only for bits corresponding for SimplifiedChineseCsbBit, TraditionalChineseCsbBit, JapaneseCsbBit and KoreanCsbBit. and in my situation value 0x97 is ignored (bits 0,1,2,4,7)

I assume that if my font had 9th bit set in signature->fsUsb, all gonna be ok, because qfontdatabase.cpp:determineWritingSystemsFromTrueTypeBits function would recognize this cyrillic bit (but font made by 3rd company, so I can't edit it). but AFAIK all zeros in signature->fsUsb has special meaning that EnumFontFamiliesEx couldn't determine these bits, so there could be any writing system.

So I think qfontdatabase.cpp:determineWritingSystemsFromTrueTypeBits must check all of signature->fsCsb bits.
and I think qfontdatabase_win.cpp:addFontToDatabase must check script value (script="Cyrillic" in my case) for True Type fonts too.

There were no problem in 4.3.0 using this font for cyrillic symbols (AFAIK there was big change in Qt font engine in 4.4.0 or 4.5.0)

I Can't attach my font because of license for it.