data0type.ic:

  Fix that 'a' LIKE 'a%' was not true for an InnoDB BLOB or TEXT type column prefix index search: InnoDB assumed that the BLOB and TEXT should not be padded with space in comparisons; this bug is also in 4.1; it may have worked in 4.1 because MySQL may have asked there for strings >= 'a', while in 5.0 it asks for strings >= 'a        '

innobase/include/data0type.ic

@@ -195,7 +195,8 @@ dtype_get_pad_char(
 	    || type->mtype == DATA_BINARY
 	    || type->mtype == DATA_FIXBINARY
 	    || type->mtype == DATA_MYSQL
-	    || type->mtype == DATA_VARMYSQL) {
+	    || type->mtype == DATA_VARMYSQL
+	    || type->mtype == DATA_BLOB) {
 
 		/* Space is the padding character for all char and binary
 	        strings */