Converting time to decimal text automatically on load - strange behaviour?

I have two excel files, seemingly formatted the same however am getting differing behaviour when trying to load with Power Query.

In both Excel files the times are formatted in the same way:

When I come to load in Power Query the first file loads as desired:

But when I come to load the second file the following appears:

I have tried turning off type detection and time intelligence but it has made no difference. Can anyone explain why this is happening and how to prevent it?

Thanks.