bug using interop to change style

Hi, I don't know if this is the place correct. I explain my problem:

I have a document with three paragraphs and various styles:

STYLES
estilo1:
FontName = Arial
Size = 12
estiloN:
....

PARAGRAPHS
1 Paragraph: STYLE (estilo1 + Times New Roman + size 10)
2 paragraph: STYLE (estilo1)
3 paragraph STYLE (Normal - default style of documents)


My selection is located in position 0 of document (1 character of 1 paragraph), then execute this code:

Dim estiloActual as Style = Me.InternalDocument.Styles("estilo1")
with estiloActual
.AutomaticallyUpdate = false
.BaseStyle = "Normal"
.NextParagraphStyle = "estilo1"
end with

This code causes a change in style in 1 paragraph. Change of "estilo1 + Times New Roman + size 10" to "estilo1".

The objective of the code from Word and pretend it does not change the results in the same outcome.
I made the same changes I intend to do in word, recording a macro and is exactly the same code I try to run, but there is no way,
for programming, do not change the paragraph style of the current selection.

Anybody can help me?

Thanks for advance.