Hello,

This is a follow-up bug-report/patch from:
https://lists.gnu.org/archive/html/auctex-devel/2025-08/msg00026.html

Previously, preview was setting the TeX-sentinel-function to temporary lambda functions inside `preview-start-*` functions which just outputs a message. This value is overwritten by functions that call `preview-start-*` to a correct sentinel. In most cases, this is harmless as the original sentinel is never called. However, preview-start-* also has a `sit-for` call which causes timers to be processed, and which may call `accept-process-output` causing the "wrong" temporary sentinel to be called.
I faced this issue when developing preview-point (discussed above) and I am submitting this patch which simply sets the correct sentinel before calling preview-start-*.

-- Al