Hello Arnold!
your extension is really great! It is almost exactly what I was searching for (and could not easily figure out how to do it). So you helped me very much.

I have a few suggestions for future development:

1, extract() works for standalone checkboxes and radio buttons, but only gets values true/false. Example: I have 3 radios named "fldA" and the third one is checked: extract() will return: {fldA:[false,false,true]}. Config option "inputValue" of the radios is not taken into account. (Compared to Ext.form.BasicForm.getValues(), which will for 3 radios return one string value specified by "inputValue" of the checked radio field.)

2, radios wrapped in Ext.form.RadioGroup are not be included in extract(). Same for CheckBoxGroup. Although I don't need "dynamic" checkboxes/radios it would be nice if extract/populate could support them.

3, horizontal alignment of the plus/minus icons doesn't work for TriggerField (requires just include of 'trigger' xtype in alignIcon())

4, populate() now requires that even the fields with blank values to be specified in the first parameter (or unlisted fields are not reset to blank values). It may be better if the loop in populate would be over all fields found in specified namespace. Example: form contais 4 fields in namespace XY, incoming parameter for populate specifies only 2 of them, populate should setup 2 listed fields and clear the 2 remaining fields.

5, it would be more intuitive for the user, if the plus icon were present always on the last clone of the specified field.
Example: master field is created with "+" icon. After the 1 clone is created, the icon for the first field changes to "-",
a "+" icon moves to the clone. That means always the last field (master or the last clone has "+") and all previous have "-" icons. But I understand, that it would be more difficult to code.