Race condition with TimeWorked updates

I have a problem with TimeWorked updates from 2 users for same ticket.
RT 4.4.1 from debian stable

0 - Ticket with XX in TimeWorked field
1 - user1 opens basic ticket info for editing
2 - user2 opens same ticket for correspond
3 - user2 write some text, write YY in TimeWorked field and press submit
4 - RT save correspondence and change ticket TimeWorked to XX+YY and add YY to user2
5 - user1 change some basic info and press submit
6 - RT save info and change TimeWorked back to XX and subtract YY min from user1 TimeWorked

I think that step 6 is incorrect and RT should not modify TimeWorked for ticket if user 2 did not modify TimeWorked
and should add correct value if user2 modify TimeWorked too.

How I can fix this race or how I can remove TimeWorked from basic info updates?