at runtime write-protected properties do not occure at self-built controls

Hallo,
I built an own activeX control to add additional properties to the textbox control.
But did anybody of you notice that ALL properties (of the textbox) that are write-protected at runtime do NOT appear in the properties list of my new control? So you cannot use this property anymore.
It is very strange!

E.g. in my case the property 'Multiline' is not shown.
And if I try to add the specific code manually, e.g. with:
Text1.MultiLine = New_MultiLine

Then the compiler throws out the error:
"Assignment to a write-protected property not possible". Strange because this equation should be possible - at design mode!!!

Or does maybe anybody know where the write-protection information is saved (so that I could deactivate it)?

Hope that anybody can explain what is going on here!?
Thank you very much.

Many greetings