mention #1874 in release notes

doc/ReleaseNotes/develop.tex

@@ -21,6 +21,10 @@
 	\underline{BASIC FUNCTIONALITY}
 	\begin{itemize}
 		\item With the LOCAL_Z option enabled, the PRT model's PRP package attempted to check that a particle release point's z coordinate fell within the grid's vertical extent before converting the coordinate from local (normalized on the unit interval) to a global (model) coordinate. This bug was fixed by converting coordinates before conducting checks.
+
+		\item The PRT model could hang upon particle termination due to no (sub)cell exit face. This occurred because a flag signaling particle advance was not set in the proper location.
+
+		\item Entangled with the previous issue, the ternary method could erroneously terminate a particle and report no exit face (before now this would hang) due to precision error in the exit time/position calculation. This could happen when two conditions are both met: the particle enters the subcell very close to one of its vertices, and flow very nearly parallels one of the subcell's faces. We have encountered similar situations before, solved by nudging the particle a small distance into the interior of the subcell before applying the tracking method. This particular case is resolved by increasing the padding distance from machine precision * 10^2 to machine precision * 10^5.
 	\end{itemize}
 
 	%\underline{INTERNAL FLOW PACKAGES}