Why is MOO trying to switch my STD to LTD after only 6 months when my policy lasts for 24?

My husband was involved in car wreck on April of 2014 where he went to a chiropractor for neck and back injuries who then referred him to get MRI’s of his neck and back on August of 2014 where he then took his MRI’s to a specialist in September of 2015 whereas at this same time, September of 2014 my husband began working for a new company where he enrolled in short-term and long-term disability policy that went into effect on november 1, 2014. In the meantime, my husbands doctor gave him injections fur his neck and back in September of 2014 where he was fine and continued to work all the way up until July of 2015 when his doctor informed him that he would need neck surgery so he went on short-term disability in August of 2015, had his neck surgery on July 28, 2015 and continued to receive his short-term disability up until January of 2016. He has not been released from the doctor as he is scheduled for back surgery now in February of 2016 so Mutual of Omaha has begun the process of switching his short-term disability to long-term disability. My question is this…does his disability need to be converted to long-term disability when short-term disability consists of 3, 6, 12 & 24 months and we have only used 6 months and need only 6 more months in order for my husband to have his back surgery then he will be released to go back to work so why is Mutual of Omaha trying to switch his short-term disability to long-term disability when the whole benefit period for short-term disability has not been used up because short-term disability consists up to 24 months then thereafter the 24 months it is then switched to long-term? Is Mutual of Omaha trying to switch his disability to long-term in order to deny his claim by saying his disability is now pre-existing?