Swallow opened the ticket and wrote:

Bug is present in r13677

When one replaces a vehicle in a depot, the order list is normally preserved. This order backup and restoration may fail for conditional order jumps in two cases:

a) The comparator used is not 'equal to' or 'not equal to'
b) The order to jump to has a higher number than the conditional jump itself.

As far I can tell, this is caused by these two lines (459/460) in order_cmd.cpp:

if (skip_to >= v->num_orders) return CMD_ERROR;
if (new_order.GetNonStopType() != ONSF_STOP_EVERYWHERE) return CMD_ERROR;

These checks may be needed when inserting orders, they cause trouble when restoring them. The order to skip to may be higher than the total number of orders because not all of them are inserted yet. Non stop flags use the same bits as the conditional comparator, which causes the second check to give problems.

Note: while I could find out what causes this. I'm not sure of the best solution. Therefore I decided to not to create a fix (yet)

Reported version: trunk
Operating system: All

This issue was imported from FlySpray: https://bugs.openttd.org/task/2130