Time machine .inprogress file creation

[ateganda29]

Hello everyone! I'm not sure if I'm on the right forum (moderators, please feel free to move to the appropriate forum if needed). I just bought a MBP 13 and wanted to do a Time Machine backup before I upgrade to El Capitan. I have a WD 1 TB external HD which I also use as my backup disk for my iMac. It successfully created a backup, however, I noticed that the supposedly temporary file of .inprogress that is created while backing up is in session remained under the backups.backupdb folder. With my iMac, the .inprogress file will be created but after the backup session is done, the .inprogress file will be deleted. That didn't happen for my backup with my MBP. I didn't get any errors or anything and when I get info/details on the file, there is nothing in it. I was able to manually delete the file, but when I run another backup, it creates one again and it won't go away after a successful backup. Can someone please let me know why this is happening, and how can I prevent it from happening? Thanks!