Defining a Drop Cap
If you define a Drop Cap in a paragraph style WITH a character style and also define a nested style, if there is a single letter word starting the paragraph, the nested style does not recognize it and will apply the nested style to an additional word beyond the deliminator. For example, a nested style through 3 words will apply to the first 4 if the paragraph starts with "I[space]" or "A[space]". It does not do this if [none] is chosen from the character style dropdown in Drop Caps, but only if one is chosen (even when nothing is defined in the character style). See attached image. Nothing is defined in chosen character style <dropcap>.
Thanks for reporting this issue.
However this behaviour seems to prevail since quite a long time.
I have marked it NeedsReview for consideration in the coming versions of InDesign.