Hi Roscoe,

The description suggests your letter 5 style doesn't have its numbering formatted to re-start after whatever the appropriate preceding Heading level is and, when you tell it manually to re-start at 'a', Word finds that the only Style for which that is applicable in the current context is the letter 3 style - to which it adjusts the format. I'm surmising that, if Word didn't do that, you could end up with both a letter 3 style and a letter 5 style with the same number level.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]