During The Name of the Doctor, we saw Clara wearing this outfit, looking out at Seven doing his literal cliffhanger from Dragonfire. For a split second, I thought she was dressed as Ace. Then I realized the jacket was all wrong. But I couldn't shake the feeling that the jacket was familiar somehow.
Then this morning it hit me: Ray from Delta and the Bannerman wears a similar jacket.
Delta and the Bannermen is the serial that immediately precedes Dragonfire.
Here's the thing: At one point Ray was supposed to be the Doctor's companion. She was created to replace Mel, but then filming and airing schedules had Bonnie Langford leaving in Dragonfire instead.
Coincidence? Oh, probably. But it's not impossible to imagine some classic Who fan on the crew geeking out and dressing Clara to resemble Ray (but not being committed to the idea enough to spend the time/money to directly match the jacket.).