pg.26, "War at Sea - South African Maritime Operations during World War 2, (CJ Harris, published 1991, ISBN 1-874800-16-2):
"...on 27 October, the DUTCH LINER TEGELBERG reported a convoy of five Vichy ships..." This is enough to convince me that she had not been converted to a troopship at that stage and was still operating on her normal South Africa/East Indies route as you suggested. She probably transported those Aussie troops to Singapore under charter as per this page:
The references listed include a book by James Burfitt titled "Against all Odds: The History of the 2/18 Batalion AIF". Perhaps one of our Aussie mates with access to this publication can confirm whether the TEGELBERG had indeed transported the 2/18.
A bit on the Vichy episode:
Following the report by TEGELBERG, an interception plan, code name "Bellringer" was implimented. SAAF Martin Maryland bombers made aerial sweeps and the entire mine clearance flotilla from Durban (HMSAS's SOUTHERN BARRIER,NIGEL,FLORIDA,TERJE,STEENBERG and STELLENBERG) was dispatched.
Smoke columns were spotted at 15H45 (GMT+2) on 1/11/1941 and the mighty force of 6 converted whalers closed at top speed, making 9 knots! They probably got the scare of their lives when they caught sight of the French escort vessel, the French navy sloop "FRANCOIS D'IBERVILLE" and her 5.5 inch guns!
The flotilla withdrew to a safe distance and shadowing continued until later that evening when big brother,the heavy cruiser HMS DEVONSHIRE showed up. The light cruiser HMS COLOMBO and AMC's CARTHAGE and CARNARVON CASTLE joined a day later. After much exchanging of signals and a few shots fired, the convoy was stopped and the French sloop stood down, returning to Madagascar. The French merchant crews attempted to set off scuttling charges and put fire to some ships but their plans were thwarted by boarding parties from the minesweepers.
The French vessels seized were: COMPIEGNE, BANGKOK, COMMANDANT DORISE, CAP PADARAN and CAP TOURANE - all claimed as prizes on the grounds of "resistence and sabotage".(Still sounds like piracy to me!)
It is quite an entertaining story but I still have a problem with the identity of the French Sloop. The book has 2 photographs clearly identifying her as a "Colonial Sloop" belonging to a class of 4 vessels built between 1931 and 1939 (DUMONT D'URVILLE,SAVORGNAN DEBRAZZA,D'ENTRECASTEAUX and LA GRANDIERRE - 2 000 tons,3 x 5.5", 4 x 40mm) No trace of a "FRANCOIS D'IBERVILLE anywhere. A false name perhaps?