1. Create a monthly repeating scheduled transaction (SX) starting today.

2. Open "Since Last Run", and change that SX status to Postponed. Click OK.

3. Open "Since Last Run". Note that the date of the SX is next month, not this month.

4. Change that SX status from Postponed to To-Create, and click OK.

Result: The transaction is created with a date 1 month in the future.

What happened to this month's transaction, which was postponed?

In the GnuCash Help manual, Chapter 8, Since Last Run Assistant, it says that Postponed means: "If a scheduled transaction has been listed with a status To-create but you want to hold it and not have it entered in your register yet, then you can set it to Postponed." Note the word 'yet'.

To Postpone is to 'put off until later'. Postponing a scheduled transaction should not skip this instance of the transaction, but should just delay it.  That is implied by the Help manual text quoted above, but that is not what GnuCash does.