--- a/aircraft_cmd.c	Sun Jun 04 17:38:48 2006 +0000
+++ b/aircraft_cmd.c	Sun Jun 04 17:49:16 2006 +0000
@@ -538,7 +538,13 @@
 		u = v->next;
 		mail = (new_cid != CT_PASSENGERS) ? 0 : avi->mail_capacity;
 		u->cargo_cap = mail;
-		v->cargo_count = u->cargo_count = 0;
+		if (v->cargo_type == new_cid) {
+			v->cargo_count = min(pass, v->cargo_count);
+			u->cargo_count = min(mail, u->cargo_count);
+		} else {
+			v->cargo_count = 0;
+			u->cargo_count = 0;
+		}
 		v->cargo_type = new_cid;
 		v->cargo_subtype = new_subtype;
 		InvalidateWindow(WC_VEHICLE_DETAILS, v->index);

--- a/ship_cmd.c	Sun Jun 04 17:38:48 2006 +0000
+++ b/ship_cmd.c	Sun Jun 04 17:49:16 2006 +0000
@@ -1061,7 +1061,7 @@
 	}
 
 	if (flags & DC_EXEC) {
-		v->cargo_count = 0;
+		v->cargo_count = (v->cargo_type == new_cid) ? min(v->cargo_cap, v->cargo_count) : 0;
 		v->cargo_type = new_cid;
 		v->cargo_subtype = new_subtype;
 		InvalidateWindow(WC_VEHICLE_DETAILS, v->index);

--- a/train_cmd.c	Sun Jun 04 17:38:48 2006 +0000
+++ b/train_cmd.c	Sun Jun 04 17:49:16 2006 +0000
@@ -1789,7 +1789,7 @@
 				if (new_cid != v->cargo_type) cost += _price.build_railvehicle >> 8;
 				num += amount;
 				if (flags & DC_EXEC) {
-					v->cargo_count = 0;
+					v->cargo_count = (v->cargo_type == new_cid) ? min(amount, v->cargo_count) : 0;
 					v->cargo_type = new_cid;
 					v->cargo_cap = amount;
 					v->cargo_subtype = new_subtype;