Because of single thread serialization, something unexpected for the programmer happens.
1) You expect TaskA to be independent from TaskB, but it isn't. If you think it is a problem of resources of the computer, change the activity frequency of 1 of the two tasks.
Suggestion: A) let the programmer choose if single thread serialization is used or not. B) keep 1 thread for 1 activity policy for default. It will help less experienced user to avoid common errors. Click below to read the rest of this post.