Explosive spear and Momentum gem

The momentum support gem gives 40% more damage to the remaining duration of a skill when moving more than 2 metres during the skill.

Unfortunately in testing Explosive spear the explosion of the lodged spear does not count as 'the rest of that use of the skill', even if you move more then 2 metres from where it was thrown.

Given the gem is compatible with Explosive spear I don't think this is working as intended.