I notice that bridge reader sets the default axle load when version is less than 5, but the version that introduces axle load in the file format is 7. Copy-paste error? (5 is correct version in tunnel reader.)
While I'm at it, the tunnel writer forgets to put aside space for has_way, which is written somewhat later than the other attributes. has_way should be at 22 and number_portals at 23, for a node size of 24, which is two bytes more than for version 4 as it should be.
Thanks, shoudl be fixed in r7058
Good thing you spotted the error in my error report.