[9fans] 9PI kernel stability

[Dante <subscriptions@posteo.eu>]

Dear 9ers,

I have noticed 2 interesting symptoms while running my Raspberry PI
(Model B, 512MB) for quite some time.
They look to me as some sort of race conditions. If anyone has seen
these before or has an idea what's wrong, please help:

1. Text windows sometimes get black "garbage" on the background that
refuses to go, even if text is scrolled over it.
     The size of the "garbage" is about 1 character, and looks like an
"island". That is, neither meaningful symbol, nor random pattern.

2. When writing large files to an USB memory stick FAT file system (say,
a large TAR archive), the mount is lost, leading to a truncated file.

Any idea how I could start debugging this?
/dev/kmesg is not verbose enough to get anything out of it.

Thanks!
Dante