Update documentation/release_6.3.htm

Co-authored-by: Kris Thielemans <KrisThielemans@users.noreply.github.com>

Author: danieldeidda

documentation/release_6.3.htm

@@ -132,11 +132,12 @@ <h3>Changed functionality</h3>
   <h3>Bug fixes</h3>
   <ul>
     <li>
-      Fixed a bug in the SPECTUB matrix (introduced in 4.0) that inverted the SPECT reconstruction along the axis.
-      This had resulted with an inconsitent attenuation correction orientation compared to the reonctructed image. 
-      The axis inversion is now reverted, so if your scripts were using an inverted attenuation map they need to be
-      updated with this release. 
-      See <a href="https://github.com/UCL/STIR/pull/1631"">PR #1631</a>" . </li>
+      Fixed a bug in the SPECTUB matrix (introduced in 4.0) that effectively inverted the "x" (horizontal) axis for the
+      attenuation image. This resulted in an inconsistent attenuation image orientation compared to the reconstructed emission image. 
+      This axis inversion is now reverted, so if your scripts are using an attenuation map, you need to ***remove**
+      calls to `invert_axis x` (or code to that effect) to get correct results.<br>
+      See <a href="https://github.com/UCL/STIR/pull/1631"">PR #1631</a>".
+      </li>
     </ul>
     <li>
       Fixed a bug in the scatter estimation code (introduced in release 5.1.0) if input data is 3D and "cylindrical"