In the .odt file "From Left" aligned tables are set at the left edge of the paragraph. "Left" aligned tables are set on the left margin, so they align with the exdented section numbers.
In the xhtml export, both types are set on the left margin. I'll provide a test case.
Created attachment 70718 [details]
Sample with "From Left" and "Left" tables
This file contains two tables. The first is "From Left" aligned. The second is "Left aligned". File > Export > XHTML this file. Observe that both tables are set on the left margin whereas in the ODT file the "From Left" table aligns with the paragraph text.
Peter Jentsch committed a patch related to this issue.
It has been pushed to "master":
fix fdo#57641 table alignment broken in XHTML export
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.
fixed on master, center alignment also fixed.