The latest attack occurred in southern Afghanistan, said the International Security Assistance Force (ISAF) headquarters in Kabul, bringing to 45 the number of foreign troops who've died this year in so-called "green-on-blue" shootings.
The attack by a man wearing an Afghan army uniform killed three soldiers from Australia and wounded two others. Thirty-six Australian soldiers have now been killed in the Afghan conflict.
Published reports in the U.S. have said American soldiers throughout the country have taken to arming themselves inside their own camps against the elusive, unexpected threat.
Col. Greg Smith, deputy commander of the Canadian training mission, said his 950 soldiers and trainers have not received similar orders — although he describes the "potential threat" of either murder or infiltration to be top of mind among the contingent.
"They are concerned about that," Smith said in a telephone interview from Kabul just prior to the latest killings.
Precautions are taken and Canadians often work in pairs along the Afghans.
Statistics compiled by NATO show some of the attacks by genuinely disgruntled Afghan soldiers have resulted from them taking offence either to their treatment or the social behaviour of western soldiers, Smith said.
The relaxed Canadian style — coupled with a reliance on their trademark sense of humour and a consistent show of respect for Afghan culture — has meant less tension with local troops, he added.
"One of things I find is that the Canadian self-deprecating manner is quite beneficial," Smith said.
"The ability to stand in front of a fellow soldier and say: 'Listen, dude. I'm a soldier. You're a soldier, in this case Afghan. I just happen to be Canadian and have a bit more experience than you and let me show you how I do it.'"
Smith's comments come as briefing documents in Ottawa suggest the slowly receding surge of U.S. forces in Afghanistan could force some Canadian troops to put down their teaching tools and pick up a gun to help with guard duties — "force protection" in military lingo — around their training bases.
The size of incoming American units has been cut in half as part of reduction of 28,000 troops ordered by U.S. President Barack Obama, a readjustment in strength that is supposed to be finished by September.
Security at the four bases in Kabul where Canadian troops conduct training and oversee the mission have one layer of private security and a second layer, which has been comprised of U.S. national guard troops.
A censored briefing note, prepared for the commander of the Canadian Army last year, pointed to the anticipated drawdown of U.S. forces and its impact on Canada and other nations involved in the NATO-led mission.
It stressed the necessity of force protection training for Canadian mentors, even though the Harper government had initially painted the assignment in the most benign of terms.
"Weapons training must make (task force) members comfortable with small arms (sic) weapons handling (censored)," said the note, written for Lt.-Gen. Peter Devlin and dated Sept. 28, 2011 — almost three months after the training contingent was activated in Kabul.
The note also suggests "increased weapons proficiency training for non-Army personnel," notably the air force mechanics and other specialized trades that are helping develop more sophisticated skills among the Afghans.
Smith said the contingent has not received a request from either NATO, or the U.S. to assume guard duties.
The majority of camps are U.S.-run; in some cases, Canadians are already picking up the odd force protection shift. Smith said it's unclear whether they'll be asked to do more.
"It is possible, but I'm not seeing a big pull towards that," Smith said.
"It's something pretty central as far as doing our job here. Before you can go out (and) advise Afghan forces in the instruction of their troops, you have to make sure you are yourself safe in the camps. So that kind of thing would not be jeopardized.
"If U.S. forces are pulling out of place, we just co-ordinate with them properly to make sure the adequate force protection is being done."
The number of Canadian troops involved in the training program is expected to dwindle as the deadline approaches for their withdrawal in March 2014.
The NATO bases have become routine targets for insurgents, including the notorious Haqqani network, a vicious splinter group of the Taliban, which has launched a series of complex attacks across the Afghan capital.
An attack on one camp near the U.S. embassy in September 2011 was repulsed by Afghan forces, with the help of Canadian trainers.