problem with big varchars and adodb

Hi,

I've got PG 8.4 on WinXP with the latest official odbc driver.
Client is Access 2000. At least for now.
ADODB connection without DSN

I was figuring out how I can store debug-infos that come as large
textfiles and tried with what string-length the insert with adodb would
crash. ;)
The default wouldn't carry far so I upped MaxLongVarcharSize to 65535
because I thought this would get me 64kb strings.

When it wouldn't break with 128kb I went further though there weren't
any errors rised even when it stopped actually storing the big string.
Every other column worked still and the tupel got created.
After 40 million chars the text gets transparently replaced by the
current date formated as '2010-04-17 00:00:00'. The timedigits are all 0.

I wouldn't mind if there gets an error thrown instead of simply replace
the bad value.

Any ideas what's happening there?