Vista - v2ctp3: Output of less.exe differs when using Parameter() attribut

I use less.exe as my preferred paginator. After installing PowerShell v2ctp3,
I've noticed some odd behavior of less.exe. I've narrowed the odd behavior
down to the following code:

function nobug
{
param(
$foo
)
less.exe c:\windows\system32\eula.txt
}

function bug
{
param(
[Parameter()]$foo
)
less.exe c:\windows\system32\eula.txt
}
On my XP PC, less.exe displays correctly with the nobug function. But the
bug function seems to have an incorrect impression of the console screen size
and displays its output primarily below the less prompt and doesn't clear the
screen correctly.

This behavior is duplicated on another VM copy of Vista as well.

I don't understand what contextual change(s) that occur while using the
[Parameter()] attribute that would cause less.exe to display different
output. Am I missing something here? Or is this some weird PowerShell bug?