Using Libreoffice 5.4.4.2 on Windows 10 with the font set to Times New Roman.
When I type in – and then hit the space bar to make the two dashes a solid line, a date of April 6 2017 is inserted into the document. if I hit a cntl-z to undo, the two dashes are visible, but not the space afterwards. I noticed this behavior with version 5.4.1 and upgrading to 5.4.4.2 did not fix it.
This seems to be a windows only bug. When running Libreoffice 5.4.4.2 on Ubuntu 16.04.3, the bug does not occur