Steps to replicate

1. Create a new PPTX file, insert a table and put some words to be searched later (e.g: Test Cheetah.pptx
2. Attach the PPTX file to a Confluence file
3. Using Confluence Search, try find the word inside the table (e.g: search for the word 'Biotechnology' that's written inside a table of the sample file above)

Workaround
Convert the file to PPT format (97-2003 Powerpoint)