[GNC] Can't complete "To-Create" scheduled transaction in "Since Last Run"

[rsbrux]

I have a scheduled transaction involving two currencies: a charge in EUR 
which is charged to  a CHF credit card.

This has worked in the past.

When the "Since Last Run" dialog appears, it lists this transaction 
under "To-Create" and shows:
EUR <-> CHF    (Need value)

When I click on "(Need value)", it turns into what appears to be a text 
edit field, where I usually enter an exchange rate.

However, today, no value was accepted, leaving me unable to close the 
"Since Last Run" dialog with "OK".

I couldn't find any relevant information in the online 
<https://cvs.gnucash.org/docs/C/gnucash-guide/txns-sxn1.html> help in 
the included help or on the wiki 
<https://wiki.gnucash.org/wiki/Scheduled_Transactions>.

How is this supposed to work?

The exchange rate is one of those which is automatically updated each 
time the computer starts.

Why can't GnuCash simply use the most recent exchange rate from the 
Price Database?

BTW, the included help  has a self-reference in the topic "Since Last 
Run Assistant": the link "Scheduled Transactions <xref:#prefs-sched>" 
links back to the same topic.

According to KDE Discover, I am running GnuCash 4.13+ released on 
2022-12-17 as a flatpak under Ubuntu Studio 22.04 LTS.

Running:

 >>

flatpak run --command=sh org.gnucash.GnuCash
[ org.gnucash.GnuCash ~]$ gnucash --version << as documented on the 
wiki <https://wiki.gnucash.org/wiki/Flatpak> produces: >> GnuCash 4.13 
Build ID: Flathub 4.13 <<