Attachment 153812 [details] from bug 127275 contains a SmartArt graphic, with Fade (in) animation defined on it. Open and save it back to PPTX.

=> PowerPoint fails to open the result cleanly.

While officeotron finds no issues in the file, OOXML-Validator points out the following:
[{"Description":"The attribute 'spid' has invalid value '-1'. The string '-1' is not a valid 'UInt32' value.","Path":{"Namespaces":{},"XPath":"/p:sld[1]/p:timing[1]/p:tnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:seq[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:animEffect[1]/p:cBhvr[1]/p:tgtEl[1]/p:spTgt[1]","PartUri":"/ppt/slides/slide1.xml"},"Id":"Sch_AttributeValueDataTypeDetailed","ErrorType":"Schema"},{"Description":"The attribute 'spid' has invalid value '-1'. The string '-1' is not a valid 'UInt32' value.","Path":{"Namespaces":{},"XPath":"/p:sld[1]/p:timing[1]/p:tnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:seq[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:par[1]/p:cTn[1]/p:childTnLst[1]/p:set[1]/p:cBhvr[1]/p:tgtEl[1]/p:spTgt[1]","PartUri":"/ppt/slides/slide1.xml"},"Id":"Sch_AttributeValueDataTypeDetailed","ErrorType":"Schema"}]

One can unzip the PPTX and pretty-print the XMLs with the following command in Linux/Cygwin:
find . \( -name "*.xml" -o -name "*.rels" \) -type f -exec xmllint --output '{}' --format '{}' \;

The problematic elements in ppt/slides/slide1.xml look like this:
<p:spTgt spid="-1"/>

Observed with LO 26.2.0.0.alpha0+ (8ea8e254a3151f5390f3a10ff156fcaf8e7c5d5c), 4.0.0.3 / Windows.