I filed a bug report and provided a small test file for this and received some excellent help resolving my issue.
Combobox changed, you are right. But combobox does now, what it should do:
Open the form for editing. Have a look at the general properties of the comboboxes. Only the combobox for text is set to “AutoFill"→"No” (and also “Hide Selection"→"No”).
I don’t know why it works with AutoFill in LO 4.2.6.2, but it doesn’t in 4.3.0.4, because it is set to “No”. Set “AutoFill” to “Yes” and it works.
Robert - Thank you very much! I completely missed those settings (probably because they were not effective in previous versions - good excuse, huh? 
I am changing the status to Resolved - Not a Bug.
John D