Currently we seem to store error values not according to OpenFormula.
OpenFormula requires us to store error values as string and not as value. See http://docs.oasis-open.org/office/v1.2/cos01/OpenDocument-v1.2-cos01-part2.html#__RefHeading__1017900_715980110
Currently we write entries like:
<table:table-cell table:formula="of:=SQRT(-1)" office:value-type="float" office:value="0">
Markus Mohrhard committed a patch related to this issue.
It has been pushed to "master":
add error to office:value-type for calc cells and fdo#51810
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.
*** Bug 37993 has been marked as a duplicate of this bug. ***