NOTE: I made another video with a more extreme demonstration.
The camshaft is locked with a Vise grip ---- See    • Subaru EJ25 timing belt guide 13145AA...  

Subaru Manual Trans (MT) belt guide 13145AA021 is necessary to prevent timing belt slippage if the engine is "forced backwards" by a manual transmission.
I have had Subaru EJs - in manual transmission vans - for 24 years - and this is the first time the problem happened to me. It's uncommon, but it is a risk.

See the other video:    • Subaru EJ25 timing belt guide 13145AA...  

As expected it is advised to keep all the components in good order, belt tensioner, idler pulley bearings, water pump & timing belt.