>>>Works on the whole page, in my case - all the textboxes, buttons etc.

I used it sometimes, both on optic properties and
on special added properties as triggers to class specific _assign
Don't recall anything weird / special needing attention
Recursing to call a method OTOH might include activeX controls as well

>>
>>Question was a text box in a container in a container addressed by the thisform.setall

As the method is documented, IMO searching for edge/break cases should be done before release
unless some weakness is documented or reproducibly known
I'd expect working only in standard vfp containership
if I go sideways like oMy.addproperty("omySpecialNeeds", createobject("mySpecialGui"))
that is the time I might add checking code or effort
>
>Now this is funny... I tried with the whole form, and everything went bold... except one listbox. Weird.

Focus probably first thing I'd check if not added in special way - vfp GUI is sometimes weird
Sometimes I had special invisible control as "focus anchor" for prog visual alter(c)ations