LO has a concept of hairline borders: borders with width 0.05pt are rendered at the minimal possible unit of the output device. XHTML export converts the 0.05pt to physical units (0.0135cm), which some browsers don't display.
Changed this to emit border-width for hairline borders as "thin" (CSS unit).
(see related fdo#57539)
Peter Jentsch committed a patch related to this issue.
It has been pushed to "master":
fdo#57575 (xhtml hairline borders), fdo#57538 - xhtml right just borders.
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.