I would go even further and see the bug in a different place - when upgrading a barracks to a sentry, the sentry should cost less than when it is built directly (however the whole building process - from nothing over barracks to sentry should maybe cost a bit more (e.g. 1 more trunk))
I would go even further and see the bug in a different place - when upgrading a barracks to a sentry, the sentry should cost less than when it is built directly (however the whole building process - from nothing over barracks to sentry should maybe cost a bit more (e.g. 1 more trunk))