Batch Convert : levels-change, resulting thumb not changed [1.9.2 W10 64b]

[meteorquake]

I ran a batch convert where I resized 75% then applied a Levels change (different levels for red and blue; my camera colour setting had got bumped so my pictures had come out rather blue)
Saving as jpeg-li, the settings said to rebuild the thumbnail.
The resulting files when opened were right (their levels were changed), but the thumbnails did not reflect the levels change and were still blue. (I used an online thumbnail viewer to double-check).
Doing the same actions manually on a photo seems to correctly rebuild the thumbnail.
1.9.2 W10 64b
Let me know if problems reproducing.
d