Bug #37813 main.variables fails randomly

Description:
Symptom 1:
------------------------------------------------------------------------
mysqltest: At line 434: query 'show global variables like 'log_warnings'' failed: 1: Can't create/write to file 'c:\tmp\pbtmp-n_mix-100\#sql_b70_0.MYD' (Errcode: 13)

The result from queries just before the failure was:
< snip >
select @@global.max_user_connections,@@local.max_join_size;
@@global.max_user_connections	@@local.max_join_size
100	200
set @a=1, @b=2;
set @a=@b, @b=@a;
select @a, @b;
@a	@b
2	1
set @@global.global.key_buffer_size= 1;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key_buffer_size= 1' at line 1
set GLOBAL global.key_buffer_size= 1;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key_buffer_size= 1' at line 1
SELECT @@global.global.key_buffer_size;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key_buffer_size' at line 1
SELECT @@global.session.key_buffer_size;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key_buffer_size' at line 1
SELECT @@global.local.key_buffer_size;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'key_buffer_size' at line 1
set @tstlw = @@log_warnings;
show global variables like 'log_warnings';

More results from queries before failure can be found in e:\var-n_mix-100\log\variables.log

Warnings from just before the error:
Error 1 Can't create/write to file 'c:\tmp\pbtmp-n_mix-100\#sql_b70_0.MYD' (Errcode: 13) 
Error 1036 Table 'c:\tmp\pbtmp-n_mix-100\#sql_b70_0' is read only
------------------------------------------------------------------------

Symptom 2:
------------------------------------------------------------------------
mysqltest: At line 714: query 'show variables like 'log_queries_not_using_indexes'' failed: 1: Can't create/write to file 'c:\tmp\pbtmp-n_mix-100\#sql_c94_0.MYD' (Errcode: 13)

The result from queries just before the failure was:
< snip >
@@ssl_ca	@@ssl_capath	@@ssl_cert	@@ssl_cipher	@@ssl_key
#	#	#	#	#
show variables like 'ssl%';
Variable_name	Value
ssl_ca	#
ssl_capath	#
ssl_cert	#
ssl_cipher	#
ssl_key	#
select * from information_schema.session_variables where variable_name like 'ssl%' order by 1;
VARIABLE_NAME	VARIABLE_VALUE
SSL_CA	#
SSL_CAPATH	#
SSL_CERT	#
SSL_CIPHER	#
SSL_KEY	#
select @@log_queries_not_using_indexes;
@@log_queries_not_using_indexes
0
show variables like 'log_queries_not_using_indexes';

More results from queries before failure can be found in e:\var-n_mix-100\log\variables.log

Warnings from just before the error:
Error 1 Can't create/write to file 'c:\tmp\pbtmp-n_mix-100\#sql_c94_0.MYD' (Errcode: 13) 
Error 1036 Table 'c:\tmp\pbtmp-n_mix-100\#sql_c94_0' is read only
------------------------------------------------------------------------

This may be related with Bug#37800.

This is *not* related to Bug#36098.

Another title for this bug may be "SHOW VARIABLES statement fails randomly".

How to repeat:
https://intranet.mysql.com/secure/pushbuild/xref.pl?testname=main.variables

See also Bug#39750.

Actually, this happens only on vm-win2003-32-a (so far almost 300 times, starting 2007-10-17). This xref is better than the above: http://tinyurl.com/49e52n

Not seen since 2009-01-16, assume HW/OS problem specific to that host.