Beat Designer Insert Pattern - Midi track corrupted after saving

Cubase 8: If I insert a pattern from Beat Designer into my midi track, it works fine until saving. On reopening it shows as an incredibly long event with one beat continuing for thousands of bars.

This is a function I’ve used for years but have only had this problem with this specific project. Works fine if I use Midi drum editor but I much prefer to use Beat Designer.

Here are the steps I’ve been doing:

  1. Create pattern in Beat Designer
  2. Choose ‘Insert Pattern at Cursor’ or ‘Fill Loop with pattern’
  3. Midi event is fine
  4. Save project
  5. Re-open project - Midi event as shown in 2nd pic - no sound triggered.

N.B. as a new user I can only insert 1 pic but the midi event is completely normal before saving.
Any advice much appreciated