TComboBox does not show focus

In a multi-form program, when a particular (subsidiary) form starts, it doesn't provide the usual indication that the TComboBox (csDropDownList) with actual control has control.
If I move focus to another control and then tab to the first control, I get the usual dotted line box inside that control.
There are a number of ON.. actions on this control, but if I add another control on the same form with no controls (and set tab order = 0) I get the same result - the new control still doesn't show that it has control.
I tried to reproduce this functionality with a simple one-form program, but it works perfectly OK.
This "feature" seems to appear in all forms in this program except the main form.
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Hi Graham,
I reread your post many times, but I am sorry, I can not understand what you mean, could you rephrase please:

I have difficulty understand the following:
with actual control has control
I get the usual dotted line box inside that control
There are a number of ON.. actions on this control
the new control still doesn't show that it has control

Could you add screenshot?
GrahamDLovellAuthor Commented:
Yes, it was difficult to describe, so have given you two pictures as you have suggested; one is not OK, but the other is OK.

It may be relevant that the focus works OK under some circumstances. eg. after using tab to move between fields.
You are correct, I can reproduce.
This is related to the theme. If you disable the runtime theme this would not happen.
You should report this to EDN.

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GrahamDLovellAuthor Commented:
Thanks. I was going around in circles on this.

I can't find "runtime themes" in Project Options. It must be obvious, or I would be able to Google it.
Which Delphi version you have there?
GrahamDLovellAuthor Commented:
Delphi menu -> Project -> Options -> select Application.

You might need to rebuild.

PS: Disabling the theme will make your application looks like it was compiled with Delphi 7.
GrahamDLovellAuthor Commented:

While I prefer the theme "look", at least I now know something about what is happening, and can make an appropriate choice.
GrahamDLovellAuthor Commented:
Thanks for your clear and helpful assistance.
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