A small puzzle ?

One of my projects recently encountered a glitch.
Its php4 and mysql3.2 on linux through apache.
The app collects a list of parts and formats a printed worksheet.
The users enter a ref number for each part which the php prefixes with a
'group' identifier (A).
The whole part ref (A1,A2,A3...) is stored with the rest of the job in the
lines table.
The display routines pull the lines in from the db and sort by left($ref,2)
so the A10 comes after the A1.

For a short period, the new entries were coming back unsorted.
This was in a period of unusually high server usage (1-2hrs) from elsewhere
in the network.

Could the database write's have been affected by the server load ? The raw
data looks ok.
Could a user have sneaked in some control chars ? Validation is v.poor (!).

New entries now are fine, the corrupted entries remain unsortable.

cheers