https://github.com/fonttools/fonttools/pull/1292#issuecomment-407427544 this is to match makeotf's behavior https://github.com/adobe-type-tools/afdko/pull/498/files#diff-17824930b3cdfb707ae56e1f42bccec6R2305
https://github.com/fonttools/fonttools/pull/1292#issuecomment-407427544 this is to match makeotf's behavior https://github.com/adobe-type-tools/afdko/pull/498/files#diff-17824930b3cdfb707ae56e1f42bccec6R2305