That's not a 90-degree-turn but the shortest and sharpest possible construction of a two-times-45-degree-turn.

This setting can be overridden on a per-railtype basis by NewGRFs,
It would probably be useful if you could include a savegame which shows the issue.

@TinCanTech At the very least, what NewGRFs do you have in your savegame?

That's not a 90-degree-turn but the shortest and sharpest possible construction of a two-times-45-degree-turn.

I presume you mean something like this:

90 degree turns are banned - 2x 45 degree bends are not ?

what NewGRFs do you have in your savegame?

#openttdcoop NewGRF package 0.8
OpenGFX+ Landscape 1.1.2

Save game - Enjoy ;-)

MAG-01, 11th Jan 3544.sav.zip

Is the train lost ?

Is the train lost ?

Something like that, I was having congestion problems ..

Forbid 90° is used when pathfinding but lost train can't find path so they don't follow the rule.

OK - That explains it, thanks!

Forbid 90° is used when pathfinding but lost train can't find path so they don't follow the rule.

This is not consistent with the code or what the setting is supposed to do. 90° detection is done outside the pathfinder as well, in track following, end of line detection, PBS reservation follow/extension, safe waiting position detection, etc. (Take a look at the call sites of Rail90DegTurnDisallowed).
The only time a train should be able to do this is if the setting is switched after the leading vehicle has already passed over the 90° turn.

For the record, I always have "Forbid trains from making 90 degree turns: On"

At zerost: Sorry for being so very short in my first comment. Writing on the phone is a pain. May the technical progress big as a whole planet, my fingers does and will not shrink to match the char-key-buttons in any way.

That's not a 90-degree-turn but the shortest and sharpest possible construction of a two-times-45-degree-turn.

At first: I was wrong with interpreting your screenshot in the opening message. I payed attention to the two sharp two-times-45-degree-curves but not to the turning train. Sorry.

I presume you mean something like this:

90 degree turns are banned - 2x 45 degree bends are not ?

At second: Sharp curves with two times 45°-turns are not affected by the setting.

Because the discussion shows that the issue seems to be independent from that take my notice only as a notice.

At first: I was wrong with interpreting your screenshot in the opening message. I payed attention to the two sharp two-times-45-degree-curves but not to the turning train. Sorry.

No problem, I should have made my 'shot more clear ;-)

the discussion shows that the issue seems to be independent from that

Agreed.

For the time being, we must accept:
There is more to detecting a 90 degree bend than to banning them.