Unable to Delete / Hide / Add columns when cells are merged
When you have merged cells on top and then unmerged cells below (merged cells will be a header for January and unmerged cells would be data points like Salary / Budget / Available) you are unable to add / remove / hide specific columns, if you select the Salary column and click hide / insert or delete excel will delete the 3 columns since they are merged together. This bug was not present in earlier verions of excel.
Alan Williams commented
This bug has returned in the latest version of Office 365. Very annoying!