This is not a bug but is a deliberate change in the SU4 beta (and also previously the SU3 beta too). This change is to allow those enrolled in the beta the opportunity to test all Career specializations and missions, not just the ones you have unlocked so far. Once the beta is over (or if you choose to manually unenroll and return to SU3), your regular career progress will be restored. This is explained in the “[READ FIRST] Welcome to the Sim Update 4 Beta!” post here:
Changes to Career/Challenge League in the Sim Update 3 Beta
Just like the recent Sim Update 3 Beta, Career and Challenge League will have separate progress and leaderboards from the live build.
This means Career mode progress in the live build will not carry over to the flighting build, and vice versa. In addition, Challenge League in the flighting build will have a separate leaderboard from the live build.
Making Career and Challenge League progress separate in the flighting build allows us to test additional changes and fixes that cannot be tested in the live build. All Career specializations will be unlocked by default in the flighting build to allow participants to preview changes that might not be available (based on Career mode progress) in the live build.
Will joining the Sim Update 4 Beta (and future Sim Update Betas) impact my progress in Career mode on the live build?
No, Career mode progress is locked to the live build. No Career progress made in the flighting build will carry over to the live build. However, all Career mode specializations are unlocked by default in the flighting build.
Beta and non Beta Careers are separate. Any progress in Beta doesn’t Impact your non Beta career progress. Beta Career is fully unlocked so all career missions can be tested during Beta.