Řešením je uvedení kratšího tvaru content-type.
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Dlouhé tvary:

"application/vnd.openxmlformats-officedocument.wordprocessingml.document" (for .docx files)
"application/vnd.openxmlformats-officedocument.wordprocessingml.template" (for .dotx files)
"application/vnd.openxmlformats-officedocument.presentationml.presentation" (for .pptx files)
"application/vnd.openxmlformats-officedocument.presentationml.slideshow" (for .ppsx files)
"application/vnd.openxmlformats-officedocument.presentationml.template" (for .potx files)
"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" (for .xlsx files)
"application/vnd.openxmlformats-officedocument.spreadsheetml.template" (for .xltx files)

Krátké tvary:
"vnd.ms-word.document.macroEnabled.12"
"vnd.ms-word.template.macroEnabled.12"
"vnd.ms-powerpoint.template.macroEnabled.12"
"vnd.ms-powerpoint.addin.macroEnabled.12"
"vnd.ms-powerpoint.slideshow.macroEnabled.12"
"vnd.ms-powerpoint.presentation.macroEnabled.12"
"vnd.ms-excel.addin.macroEnabled.12"
"vnd.ms-excel.sheet.binary.macroEnabled.12"
"vnd.ms-excel.sheet.macroEnabled.12"
"vnd.ms-excel.template.macroEnabled.12"