When more than one workplace switcher is used, only one will show the specified number of rows, instead using only one row. This can be quickly repaired in session by opening the affected switcher's properties than closing it. The attachment show two switchers on separate panels when Desktop is opened.
Created attachment 8893 Two workplace switchers showing one with number of rows '2' not used
Indeed, I can confirm the bug. I'm not sure it's in the panel though, I need to investigate further. libpager-Message: 00:00:32.896: Setting the pager rows returned false. Maybe the setting is not applied. libpager-Message: 00:00:32.897: Failed to set the number of pager rows. You probably have more than 1 pager in your panel setup. This means that the call to wnck_pager_set_n_rows fails. From reading the code (and documentation) about that call only one pager widget should try to set the rows (i.e. you shouldn't really be able to configure two pager widgets differently consistently). https://gitlab.gnome.org/GNOME/libwnck/blob/master/libwnck/pager.c#L2330 Did this work for you consistently in 4.12?
I know it didn't work in 4.14pre2.
*** Bug 15833 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 11831 ***