Libreoffice version 5.x and 4.x If you insert an image with the upper left corner in cell A1, and then position the image such that its left edge is right up against the left edge of the spreadsheet, and then save the spreadsheet, then when you re-open the spreadsheet there is about a 1mm gap between the edge of the spreadsheet and the edge of the image. This does not happen in MS-excel. (Saving using xlsx format) Note that this does not happen with ODF format, but unfortunately most of my customers still use excel...
I just noticed that Libreoffice on Windows does not have this problem.
Please attach .ods file. After resave as .xlsx should bug occur?