Worked example.

Two parallel bookings.

Friday > Monday

Satruday > Monday

I try to add in bike M3 to the second booking.  BRM rightly detects the clash and doesn't allow:

Then I go back to the first booking - the blue one - and check it in early.  On Saturday:

Reservation goes Green.

Bike M3 is made available upon check in.

Then I go back to the second booking and add in M3 which now works: