Percentage increasing by 100

Hi all,

I have an issue where, when inputting a percentage into the %Complete column which accompanies the Gantt, it multiplies this percentage by 100! I.e. it turns 1 into 100% and 100 into 10,000% - screwing with the sheet.

The strange thing is, this is only happening for one of my team. When i do it, in the exact same cell, 1 = 1 and 100 = 100. The only difference between us is a license but i havent come across this issue before so not sure thats the cause...any ideas? Checked personal settings of the individual etc and they are no different to mine.