And
now I remember why I had that silly option checked in FPCUpDeluxe.
See also
this fix in a German Lazarus forum - which indicates this error has been observed under Linux as well.
In short, to fix the synhighlighterpython.pas error:In the file "
../lazarus/components/synedit/synhighlighterpython.pas", change line 549
HEXCHARS = ['a' .. 'f', 'A' .. 'F'] + INTCHARS;
to
HEXCHARS = ['a' .. 'f', 'A' .. 'F', '0' .. '9'];
Back to the problem (TComboBox) at hand; Your fix works! Tested in the small test project and my larger project - no more Access Violation errors

Lazarus 4.99 (rev main_4_99-2073-g15a44331c3) FPC 3.3.1 x86_64-darwin-cocoa
Thank you Rich2014!