It's a "leak" only if it creates problems for you, such as slowdown or risk of running out of memory. In this case, there are no such problems - memory use and execution time are both bounded. The memory gets automatically reclaimed when the program restarts (that's the job of the OS, and if it fails at it, you can always reboot the machine).

It's a perfectly fine way of engineering a system.

There's also a variant of this that's been used on missiles - basically, you put enough RAM on the weapon to guarantee it'll hit its target or run out of fuel before running out of memory.