kim ucyate bhavān?
Enter Sarvārthasiddha of Maitrīpura mahāvihāra (the Kwa Bahal of Kathmandu just within the old city**) affixing this note to a manuscript of the Caṇḍamahāroṣaṇa now kept in the Bodleian Library (ms. Hodgson 2). Note that it was probably great weather in āśvina 1823 as the monsoon just ended, so bad Sanskrit is not to be put down to the rain.
yadā dṛṣṭaṃ tadā likhitaṃ lekhako nāsti doṣakaṃ |
jadi śuddhaṃ m-aśuddhaṃ vā śuddhanīyo mahadbudhīḥ ||
When (i.e. the way) I saw it then (i.e. just the same way) I wrote it, there ain't no fault with the scribe! If anything is clear or unclear [in the readings], the big-headed ones correct it!
Sorry for the colloquial translation, I just couldn't resist. It's a bit puzzling (amongst many other things) why the wise ones should correct good readings. But this seems to have been a trope. Here's another one from 1281 māgha (again nice and cool weather):
jādisaṃ pustakaṃ dṛṣṭā tādisaṃ likhitaṃ mayā |
jadi sudham asudhaṃ vā mama dokho na dīyate ||
udakānalacorebhyo musikebhyo tatheva ca |
rakṣatavya payatnena mayā kaṣṭena likhite ||
I wrote this just the way I saw it in a book. If anything is clear or unclear [in the readings], don't put the blame on me! I copied it in the midst of hardships, so it should be kept away from water, fire, thieves, and mice.
This guy was particularly bad: he even managed to misspell the name of his king (Anaṃtamīla for Anantamalla) and wrote 'Thoysday' for 'Thursday' (vyaśapati for bṛhaspati).
And there are doubtless many more. Please feel free to add your finds.
* I heard the anecdote from Prof. Sanderson.
** The fact that this Bahal is still within city bounds is Kashinath Thamod's discovery.