Active X text boxes on my sheet are being recognized as pictures?

I have had this problem many times and when I think I have fixed it, it come back. I have two text boxes on my sheet that I am using as a log in sheet. I am not sure what triggers them but they stop allowing me to type in them to log in and instead are recognized by excel as pictures and ask me if I want to format them. I have fixed them in the past by deleting them and adding new Active X text boxes to the sheet but then after a while they turn back into pictures. I might be doing something silly or obviously wrong but I cant work it out please help.

By the way the text boxes have been named T1 and T2 and are used in VBA behind the scenes to determine if the details that are typed into them match existing accounts if this helps in any way.

Hmm well I am using Excel 2013 at the moment and have newly switched from 2011 but it also used to happen while using Excel 2011 only. It would just happen after I had saved the system and had come back and opened it at a later date.