[marco_kellershoff]

It's more a quick hack than a good solution, but it should work:

AdminCP -> Styles & Templates -> .. choose your template .. -> Edit Templates (from Dropdown) -> User Profile Field Templates (doubleclick) -> userfield_textbox (doubleclick)

Yours should read something like this:

<input type="text" class="textbox" name="userfield[{vb:raw profilefieldname}]" id="cfield_{vb:raw profilefield.profilefieldid}" value="{vb:raw profilefield.currentvalue}" maxlength="{vb:raw profilefield.maxlength}" />

just add the following to it:

style="height:auto!important;"

So in the end it should look something like this:

<input type="text" class="textbox" name="userfield[{vb:raw profilefieldname}]" id="cfield_{vb:raw profilefield.profilefieldid}" value="{vb:raw profilefield.currentvalue}" maxlength="{vb:raw profilefield.maxlength}" style="height:auto!important;" />

Keep us posted if it worked for you