Behodar:
There's a name for that; Fermat's Last Post.
"A post to a bug tracker, mailing list or forum in which the author claims to have found a simple fix or workaround for a bug, but never says what it is and never shows up again to explain it (even after others have been puzzling over the bug for years)."
Thanks for hint - the existence of this theorem (despite it's mathematical use for sure) was really new to me!