When exporting to .ODT, text in bold & italic is not exported correctly

Steps to reproduce

1. Edit a page with CKEditor
2. Insert a text and format it, make it bold& italic or italic&bold
3. Save the page and export it to .odt
4. check the .odt file

Expected results

The text is properly displayed, according to the chosen format, both format styles are taken into account.

Actual results

Only the first formatting is taken into account.​​​​​​​{}

For example:

"This is bold italic"   becomes only bold
"This is italic bold" **  becomes only italic

Notes:

•  the problem only reproduces on the export of Office files (.odt and .rtf). In PDF and HTML, both formatting styles are taken into account.
• the problem only reproduces for bold and italic. Tested with Strikethrough and Underline, the display in the exported files is correct. 

Tested on wiki versions 16.10.9 and 17.4.2.