commit 26d8e9052f2226508d076f390162afb04d737bec
Author: erouault <erouault>
Date:   Sat Dec 27 15:20:42 2014 +0000

    * libtiff/tif_dir.c: in TIFFDefaultDirectory(), reset any already existing
    extented tags installed by user code through the extender mechaninm before
    calling the extender callback (GDAL #5054)

diff --git a/libtiff/tif_dir.c b/libtiff/tif_dir.c
index ab43a28..1a413df 100644
--- a/libtiff/tif_dir.c
+++ b/libtiff/tif_dir.c
@@ -1322,8 +1322,20 @@ TIFFDefaultDirectory(TIFF* tif)
 	tif->tif_tagmethods.printdir = NULL;
 	/*
 	 *  Give client code a chance to install their own
-	 *  tag extensions & methods, prior to compression overloads.
+	 *  tag extensions & methods, prior to compression overloads,
+	 *  but do some prior cleanup first. (http://trac.osgeo.org/gdal/ticket/5054)
 	 */
+	if (tif->tif_nfieldscompat > 0) {
+		uint32 i;
+
+		for (i = 0; i < tif->tif_nfieldscompat; i++) {
+				if (tif->tif_fieldscompat[i].allocated_size)
+						_TIFFfree(tif->tif_fieldscompat[i].fields);
+		}
+		_TIFFfree(tif->tif_fieldscompat);
+		tif->tif_nfieldscompat = 0;
+		tif->tif_fieldscompat = NULL;
+	}
 	if (_TIFFextender)
 		(*_TIFFextender)(tif);
 	(void) TIFFSetField(tif, TIFFTAG_COMPRESSION, COMPRESSION_NONE);