Ghost 15 Running "missed" new Base Backup results in incremental one instead

I have Ghost 15 configured to run a new base backup on the 1st and 16th of each month, and incremental backups twice each week. Every once in a while (for reasons unknown), it will miss a scheduled base backup. If I tell it to run the missed backup, I don't get a new base, I end up with another incremental. These incrementals will continue back on schedule, and the only way for me to get a new base is to delete everything and start from scratch.

 

Any idea what's going on? How do I get the missed base backup to run?

 

Thanks.

 

Ken